Abstract: A communication system in which a control microcomputer (1) for an electronic device and a peripheral device thereof are connected with each other with less signal lines by using serial communication interface function (SIO) integrated in a microcomputer, wherein since an accessing request signal (REQ signal:first signal) from the control microcomputer (1) to a communication IC (3) is also used as a response signal to an access request signal from the communication IC (3) to the control microcomputer (1), and on the contrary, all accessing request signal (INT signal:third signal) from the communication IC (3) to the control microcomputer (1) is also used as a response signal to an accessing request signal from the control microcomputer (1) to the communication IC (3), the number of control signals can be reduced.