To measure the rotational torque of a minutely rotating body with high accuracy and high resolution by calculating an area of object recognized in a recognization region, and comparing an upper limit and a lower limit of the area of object recognized.

This device comprises a rotation stage 13 rotating an object W to be measured; a supporting and fixing part 17 on which a coil-shaped spring 18 that detects a torque is mounted; a light source 27 illuminating the spring part; a camera 24 which recognizes a rotation angle of the spring 18; an X-Y stage 14 for adjusting an optical axis of the camera 24; and a fixing base for fixing them. With the constitution, for image processing angle reading means for reading a minute rotation angle of the object W, a binary means, recognition region setting means, calculating and comparing means for the area of the object to be recognized W, means for calculating and comparing longitudinal and lateral differences, and operational means for operating an angle difference with a measurement value just one before are used, whereby the rotational torque of minutely rotating body can be measured with high accuracy and high resolution, and differences or scattering by users can be reduced to thereby improve the reliability of measurement.