PURPOSE: To enable to perform data delivery with a simple constitution, by stopping the power supply of the power supply source to the slave station from the master station for a given time every one period, developing pulses of the slave station immediately after the next power supply, and using the pulse as the synchronizing signal.

CONSTITUTION: The master station 1 and the slave station 2 are mutually connected with the power supply line 3 and the signal line 4. The master station 1 stops the supply of the power supply signal A1 by the power supply source 3 to the slave station 2 ahead the data delivery for a given time T3 every one period, the slave station 2 immediately after the next power supply develops the pulse of the signal B, and the data delivery is made with the signal line 4 for the main station 1 and the slave station 2 by taking this as the syncronizing signal. Thus, with a simple costitution, the synchronism between the master and slave station can be taken, allowing to perform the data delivery.