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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-04-04</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001190158</rptOwnerCik>
            <rptOwnerName>LIM LINDA Y C</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>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2005-04-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>10.375</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12404.9569</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (Right-To-Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>10.375</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2005-04-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>4000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2003-04-30</value>
            </exerciseDate>
            <expirationDate>
                <value>2012-10-31</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Woodhead Industries, Inc. Common Stock, $1 Par Value</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">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>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert J. Tortorello for Linda Y. C. Lim by Power of Attorney previously filed.</signatureName>
        <signatureDate>2005-04-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-04-04
0000108215
WOODHEAD INDUSTRIES INC
WDHD
0001190158
LIM LINDA Y C
3 PARKWAY NORTH, SUITE 550
DEERFIELD
IL
60015
1
0
0
0
Woodhead Industries, Inc. Common Stock, $1 Par Value
2005-04-04
4
M
0
4000
10.375
A
12404.9569
D
Stock Option (Right-To-Buy)
10.375
2005-04-04
4
M
0
4000
0
D
2003-04-30
2012-10-31
Woodhead Industries, Inc. Common Stock, $1 Par Value
4000
0
D
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).
Robert J. Tortorello for Linda Y. C. Lim by Power of Attorney previously filed.
2005-04-05