PURPOSE: To realize easy quantitative detection of swing-level, by installing a coil spring, one end of a cylindrical vessel being fixed and the other end fixed with a weight and measuring a displacement of the spiral spring on the occasion of swinging.

CONSTITUTION: On one end surface of a cylindrical vessel 1, one end of a coil spring 2 is attached and on the other free end, a weight 3 is fastened. Upon swinging a rod-shaped article, the weight 3 displaces in the right direction under a centrifugal force. A light source 31, light sensor pair 32 attached to the weight displace also, changing a position in which a slittled board 4 is flashed with a roy of light. By counting the pulse numbers from the sensor 32, the position of the weight 3 is detected for measuring the swing-level.