PURPOSE: To perform a message control only when an object to be detected moves in the specified direction as desired by outputting a detection signal only when the object moves in the specified direction.

CONSTITUTION: When first and second receiver sections 10 and 20 detect an object 100 to be detected, indicators 70 and 80 light to indicate it. A computing circuit 50 performs a specified processing of detection signals from the first and second receiver sections 10 and 20 in the order of reception and outputs signals to effect a message control only when the object moves in the specified directions A and B. A switch 60 is provided to select the moving direction of the object 100 being detected which is to be checked for by the computing circuit section 50.