PURPOSE: To attain excellent transmission efficiency of information by placing an own station index number to the head of a signal using an index number so as to minimize the time required for detection of collision when collision takes place.

CONSTITUTION: When two devices 13, 14 to be controlled transmit an informing instruction representing the change of simultaneous ON to a controller 16, the index number of the controller 16 and the devices 13, 14 to be controlled is set respectively as 000, 001 and 010, and the ON informing instruction 111, the own station index, instruction and other station index number are transmitted in order. Then the devices 13, 15 transmit respectively waveforms J(001111000), K (010111000), and when they collide with each other on a lighting line 12, a waveform L is formed and it is detected at a point of time of a clock M. Thus, the collision is detected earlier.