PURPOSE: To execute automatically an inspection, by rotating a master gear and a gear to be measured, in a state that the master gear is pressed against the gear to be measured, at the time of a measurement, and measuring the displacement of the master gear caused by a bruise, etc., by a displacement measuring device.

CONSTITUTION: A gear to be measured 1 is rotatably held at a measuring position, and on the other hand, is rotatably installed to an L-shaped supporting frame 21 for supporting rockably a master gear 20. Also, a measuring device 35 for detecting the displacement is provided on the other arm of the L-shaped supporting frame 21. In this state, at the time of a measurement, the master gear 20 is pressed against the gear to be measured 1, and in this state, both of them are otated, and displacement of the master gear 20 caused by a bruise, etc. is measured by the measuring device 35, and is fetched as an electric signal.