PURPOSE: To reduce a signal line by outputting a status signal from a transmitting side to a receiving side through a data line, and transmission serial data from the transmission side as synchronizing with a clock signal from the reception side being returned as responding to said status signal.

CONSTITUTION: The reception side is provided with a means 16 to output the clock signal of prescribed number to a clock signal line 13, and the means 17 to input the serial of the data line 12 as synchronizing with the clock signal, and the transmission side is provided with the means 14 to output the status signal to the data line 12 at the time of no output of the clock signal, and the means 15 to output the serial data to the data line 12 as synchronizing with the clock signal being returned as responding to the status signal, and the reception side inputs the serial data synchronizing with the clock signal being outputted from the transmission side, as synchronizing with the clock signal. Thus, since one data line 12 can be used both for a data signal and the status signal, the number of the lines required for communication can be reduced.