A communication system has a first communication device, and a second communication device conduct wireless communication with the first communication device. The first communication device has a first transmitter that transmits a signal to the second communication device, and a first transmission controller that controls the first transmitter. The second communication device has a first receiver that receives the signal from the first communication device, a first reception controller that controls the first receiver, a signal processor that processes the signal received by the first receiver, and a determination part that determines whether the signal received by the first receiver is a normal signal. When transmitting a predetermined first signal, the first transmission controller divides the first signal into a plurality of segments to change a transmission frequency of the first transmitter in units of segments.