PURPOSE: To make possible torque measurement of a step motor for wristwatches in the state of finished assembly by detecting the displacements with time of the second hand position.

CONSTITUTION: The power of a step motor 1 drives the second hand 4 by way of a wheel train such as a pinion 2 and a gear 3. The position of the second hand 4 is detected with a camera 5 built therein with an image sensing element to make possible to regure measurement of the step motor 1. Here, if the position (x) in the circumferential direction of the second hand 4 is detected with time by the camera 5 incorporated with the image sensing element, then it becomes possible to calculate the torque which has reduced friction torque L from the shaft torque T of the step motor 1.