PURPOSE: To let the movement of the respective section of a racket be reproduced after a swing is over, and thereby make it possible to judge whether or not the swing is acceptable by monitoring the movement of the racket by means of signals detected by acceleration sensors mounted on the racket.

CONSTITUTION: Semi-conductor acceleration sensors shall be installed on the joint section 41 of a racket 40, the both side sections 41 of a frame, the top section 43 if the frame and the like. When a set of the sensors is used wherein the acceleration sensors 51 and 52 are arranged in such a way that the main detecting direction shall be maintained at an angle of θ=90°, acceleration in two directions can be detected simultaneously. And initial speeds at the time of starting a swing. Speeds at several positions in the middle of the swing, and speeds and acceleration at the time of last shot are detected by the acceleration sensors. Then, these detected data are compared with the standard data stored in a memory so as to be operated. The result of the operation allows, for example, messages to be indicated on a display device 44 embedded into a grip section.