A communication system equipped with a communication apparatus for transmitting a transmission signal to another communication apparatus via a communication medium, includes: transmission means for transmitting the transmission signal to the other communication apparatus via the communication medium; detection means for detecting a propagation signal propagated through the communication medium each time a predetermined amount of the transmission signal is transmitted from the transmission means; signal collision judgment means for judging from the propagation signal detected by the detection means whether a signal collision occurs on the communication medium between the transmission signal transmitted from the transmission means and another signal transmitted from the other communication apparatus; and control means for controlling transmission of the transmission signal from the transmission means in accordance with a judgment result by the signal collision judgment means.