When a power supply switch is turned on and an RF signal and an LO signal are input to a bipolar transistor, a mixed signal of both signals is output as an IF signal. When the power supply switch is turned off, the bipolar transistor operates as two diodes connected between a base terminal and an emitter terminal and between the base terminal and a collector terminal. When the IF signal and the LO signal are input, the input signals are mixed with each other by the diodes and the RF signal is output. Accordingly, one frequency conversion has a plus conversion gain and when bidirectional frequency conversion is performed by the use of one frequency converter, an external circuit such as a signal path switching switch is not necessary.