A reception carrier wave, of which a frequency fL0 agrees with a frequency fRX of a reception wave, is generated, a first transmission carrier wave, of which a frequency fL1 is equivalent to twice of a difference value between the reception frequency and a frequency fTX of a transmission wave, is generated, and a second transmission carrier wave of which a frequency fL2 is equivalent to a difference value between the frequency fL0 and the frequency fL1, is generated. The reception carrier wave is mixed with the reception wave to produce a reception signal. The frequency of the first transmission carrier wave is halved, and the first transmission carrier wave is mixed with a transmission signal to produce a modulated wave. The second transmission carrier wave is mixed with the modulated wave to produce a transmission wave. Therefore, because either the frequency of the first transmission carrier wave or the frequency of the second transmission carrier wave does not agree with each of the frequency of the modulated wave and the frequency fTX, the degradation of the modulation precision on a transmission side can be prevented. Also, because the frequency of the first transmission carrier wave is halved, the interference of the first transmission carrier wave with the transmission signal band can be reduced.