PURPOSE: To exactly recognize a VDT working time, by emitting a calling wave from a master station at the front of a VDT, detecting it by a slave station held by an operator engaging in a VDT work, and returning a response wave including a bit of slave station discrimination information to the master station at every detection.

CONSTITUTION: A response wave emitting means 3 is attached on the breast of an operator, and the calling wave emitting means 1 emits a very weak calling wave having directivity to be received only by a response wave generating means 3 held by the operator engaging in the VDT (video display terminal) with a prescribed cycle. The response wave generating means 3 emits the response wave including its own ID code at every reception of the calling wave. A response wave reception processing means 5 receives the response wave, and finds and stores VDT work managing information such as the starting and completing time of the work of the operator, and an accumulated working time, etc. In such way, it is possible to obtain the managing information of the VDT work automatically without spending a troublesome time.