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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-12-02</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>2005-12-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>7000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28406.685</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>750</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Wife as Custodian for Son/UGMA</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>750</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Daughter</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock award under the Company's 1999 Stock Awards Plan.</footnote>
        <footnote id="F2">Price is not applicable to acquisition resulting from grant of restricted stock.</footnote>
        <footnote id="F3">In connection with the Stockholder Rights Plan adopted by the Company on April 24, 1996, Preferred Stock Purchase Rights were distributed to stockholders and are deemed to be attached to the shares of Common Stock of the Company listed on this Form. If and when the rights become exercisable, the holders initially would be entitled to purchase one one-thousandth of a share of Preferred Stock at a purchase price of $65.00 (both the number and shares and the purchase price are subject to adjustment).</footnote>
        <footnote id="F4">Includes 377.685 shares allocated to Mr. Tortorello's account in the Woodhead Industries, Inc. Profit Sharing and Savings Plus (401K) Plan.</footnote>
        <footnote id="F5">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>2005-12-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-12-02
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
2005-12-02
4
A
0
7000
A
28406.685
D
Woodhead Industries, Inc. Common Stock, $1 Par Value
750
I
By Wife as Custodian for Son/UGMA
Woodhead Industries, Inc. Common Stock, $1 Par Value
750
I
By Daughter
Restricted stock award under the Company's 1999 Stock Awards Plan.
Price is not applicable to acquisition resulting from grant of restricted stock.
In connection with the Stockholder Rights Plan adopted by the Company on April 24, 1996, Preferred Stock Purchase Rights were distributed to stockholders and are deemed to be attached to the shares of Common Stock of the Company listed on this Form. If and when the rights become exercisable, the holders initially would be entitled to purchase one one-thousandth of a share of Preferred Stock at a purchase price of $65.00 (both the number and shares and the purchase price are subject to adjustment).
Includes 377.685 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
2005-12-06