<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-08-04</periodOfReport>

    <issuer>
        <issuerCik>0000108215</issuerCik>
        <issuerName>WOODHEAD INDUSTRIES INC</issuerName>
        <issuerTradingSymbol>WDHD</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001184369</rptOwnerCik>
            <rptOwnerName>TORTORELLO ROBERT</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3 PARKWAY NORTH, SUITE 550</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DEERFIELD</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60015</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP, Gen. Counsel &amp; Secretary</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>21463.05</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>750</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Wife as Custodian for Son/UGMA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2006-08-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>U</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>750</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>19.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Daughter</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes 434.05 shares allocated to Mr. Tortorello's account in the Woodhead Industries, Inc. Profit Sharing and Savings Plus (401K) Plan.</footnote>
        <footnote id="F2">The reporting person disclaims beneficial ownership of all securities held by his daughter and son (under UGMA), and this report should not be deemed an admission that the reporting person is the beneficial owner of such securities for purpose of Section 16 or for any other purpose.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert J. Tortorello</signatureName>
        <signatureDate>2006-08-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2006-08-04
0000108215
WOODHEAD INDUSTRIES INC
WDHD
0001184369
TORTORELLO ROBERT
3 PARKWAY NORTH, SUITE 550
DEERFIELD
IL
60015
0
1
0
0
VP, Gen. Counsel & Secretary
Woodhead Industries, Inc. Common Stock, $1 Par Value
2006-08-04
4
U
0
21463.05
19.25
D
0
D
Woodhead Industries, Inc. Common Stock, $1 Par Value
2006-08-04
4
U
0
750
19.25
D
0
I
By Wife as Custodian for Son/UGMA
Woodhead Industries, Inc. Common Stock, $1 Par Value
2006-08-04
4
U
0
750
19.25
D
0
I
By Daughter
Includes 434.05 shares allocated to Mr. Tortorello's account in the Woodhead Industries, Inc. Profit Sharing and Savings Plus (401K) Plan.
The reporting person disclaims beneficial ownership of all securities held by his daughter and son (under UGMA), and this report should not be deemed an admission that the reporting person is the beneficial owner of such securities for purpose of Section 16 or for any other purpose.
Robert J. Tortorello
2006-08-08