To improve the transmission/reception separation degree of transmitting frequency two waves and receiving frequency two waves by assigning a transmission frequency and a receiving frequency to bands which are not adjacent to each other and setting two transmitting frequencies which are to be used in single equipment to be at a distance equal to or larger than the specific multiple of a transmission signal band from each other.

In a series of communication equipment 21 to 29 to be used for a communication line for executing fully duplex communications while executing relay transmission, an available frequency band is divided into proper widths, a channel frequency is set to each of this band, and a transmitting frequency and a receiving frequency are assigned to the channel frequency of the bands after division, which are different from each other. Two transmitting frequencies to be used in a single device are set with a distance, which is equal to or larger than two-fold, e.g., three-fold, from each other. Then, when a series of communication equipment 21 to 29 executing relay transmission repeatedly use limited frequencies, an interval between the series of communication equipment which comes to generate unnecessary waves to exert influence to each other because of using the same frequency is maximized.