PURPOSE: To simplify and to economize the transmitter-receiver and to facilitate the frequency conversion by allowing a circulator in each of a transmission section and a reception section to pass a signal to one BPF twice so as to reduce number of BPFs.

CONSTITUTION: A RF signal is given to a circulator 4A of a transmission section and a BPF 5 attenuates an image signal of the RF signal and a leakage signal of a transmission local oscillator. The resulting signal is power-amplified to a required power by a power amplifier 3 via a circulator 4B, and outputted as a transmission RF output via the circulator 4B, and again the transmission BPF 5 and the circulator 4A. A reception RF input signal is given to a circulator 4C in a reception section and a BPF 6 attenuates a reception image signal and an undesired out-band signal. Moreover, the result is mixed with an output of a reception local oscillator 9 by a reception mixer 8 via a circulator 4D, a pre-stage high frequency amplifier 7, the circulator 4D and again the reception BPF 6 and the circulator 4C, and the result is converted into an IF frequency and outputted as a reception IF output.