This three-stitch dimension measuring device is provided with: an extraction unit that extracts a feature part on the outer shape of a worm gear to be measured for three-stitch dimensions; an adjustment unit that adjusts the worm gear to a state where the feature part is disposed at a prescribed position; and a measurement base that is fed with the worm gear adjusted in state by the adjustment unit, that includes a gauge provided for measuring the three-stitch dimensions of the fed worm gear so as to be able to come into contact with/separate from a screw groove formed in a screw part of the worm gear, and on which the three-stitch dimensions of the worm gear are measured in a state where the gauge is disposed in the screw groove.
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