Abstract: A communication device includes a communication connector, a communication control circuit, and a common mode filter. The communication control circuit controls communication that is established by way of the communication connector. The common mode filter is connected to each of the communication control circuit and the communication connector to relay the communication. Letting a wavelength corresponding to a clock frequency of an electric signal sent out from the communication control circuit be denoted as ?, an electrical length of a signal path at which resonance is produced by a reflected wave resulting from reflection of the electric signal by the common mode filter is closer to an even multiple of ?/2 than to an odd multiple thereof.