In a communication system for performing serial communication between a transmitting device and a receiving device, the transmitting device transmits, to the receiving device, a first data signal including at least information on a transmission clock in one frame, and transmits, to the receiving device, a second data signal including at least information on the transmission clock in one frame, during a time period from transmission of the first data signal until transmission of the first data signal in the next transmission cycle. The receiving device receives the first data signal and the second data signal transmitted from the transmitting device.