A waveguide for separating a high-frequency transmission signal and a high-frequency reception signal on the basis of their frequencies is formed in a diplexer. Further, a transmission-side connection port, a reception-side connection port and an antenna connection port are formed in peripheral portions of the diplexer such that the ports communicate with the waveguide. A circuit section including a high-frequency transmission circuit, a high-frequency reception circuit, and direct-current circuits are mounted on one side of the diplexer. The high-frequency transmission circuit is connected to the transmission-side connection port of the diplexer, and the high-frequency reception circuit is connected to the reception-side connection port of the diplexer.