A communication device calculates a signal travelling time indicating a time period from a first time at which the signal has been transmitted from the communication device, to a second time at which the transmitted signal is expected to arrive at another communication device serving as a communication partner. The communication device retransmits the signal to the another communication device when a retransmission request of the signal is received from the another communication device after the signal has been transmitted to the another communication device, and suspends a retransmission of the signal when the retransmission request is received again from the another communication device before the signal travelling time elapses from the first time.