Upon application of an on-state voltage to a control terminal, an antenna switch provided between an antenna terminal and a transmission terminal is turned on, and a transmission signal of a PCS/DCS system passes from the transmission terminal through the antenna terminal. At this time, a booster circuit, to which a part of the transmission signal is supplied, generates at an output terminal a boost voltage higher than a control voltage output from a controller due to the rectification of diodes, and applies the same to the gate of a transistor circuit of the antenna switch. Since in the booster circuit a resistor is coupled to the output terminal, the passage through resistors of an input transmission power in an RF signal path is only the passage through one resistor, thus reducing the attenuation of the transmission signal and providing an excellent insertion loss characteristic.