<?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>0001185154</rptOwnerCik>
            <rptOwnerName>NOGAL JOSEPH P</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>V.P. Treas/Contr &amp; Asst Secty</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>4000</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7815.959</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted stock award under the Company's 2001 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 315.959 shares allocated to Mr. Nogal's account in the Woodhead Industris, Inc. Profit Sharing and Savings Plus (401K) Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Robert J. Tortorello for Joseph P. Nogal by Power of Attorney previously filed.</signatureName>
        <signatureDate>2005-12-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2005-12-02
0000108215
WOODHEAD INDUSTRIES INC
WDHD
0001185154
NOGAL JOSEPH P
3 PARKWAY NORTH, SUITE 550
DEERFIELD
IL
60015
0
1
0
0
V.P. Treas/Contr & Asst Secty
Woodhead Industries, Inc. Common Stock, $1 Par Value
2005-12-02
4
A
0
4000
A
7815.959
D
Restricted stock award under the Company's 2001 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 315.959 shares allocated to Mr. Nogal's account in the Woodhead Industris, Inc. Profit Sharing and Savings Plus (401K) Plan.
Robert J. Tortorello for Joseph P. Nogal by Power of Attorney previously filed.
2005-12-06