PURPOSE: To make the mounting of a built-in type wiring instrument to a mounting frame in freely attachable and detachable by integrating an air conditioner or the like capable of corresponding to a telephone control system in a remote supervisory control system as a load.

CONSTITUTION: A case 30 is formed to the dimension of one series module of a standardized ready-made wiring instrument. The inside space of a body 31 is split by a partition 33 and an empty space at the side of one end comprises a housing part 35 housing a printed circuit board 34 in which the parts of a circuit are mounted and which is formed with the above mentioned circuit. The bottom face of the containing part 35 is formed with a terminal mounting part 39 mounting connection terminals T1, T2 to which a signal line 4 is connected. A cover 32 is formed with a light transmission/receiving window 61 for a light transmission/receiving element 27 of a light transmission circuit 22 and a light receiving circuit 21 by swelling the central part in the breadthwise direction to a shape approximately corresponding to the opening of a mounting frame 40. Control terminal equipment is embedded in a wall or the like with a rectangular frame covering the circumference of the swelled part of the cover 32. Thus, embedding into the wall or the like can be easily executed.