An object of the present invention is to allow the
miniaturization of a mobile communication equipment and the reduction of consumption power, and to improve the electrical characteristics of a final stage
amplifier. An inputted RF
signal is amplified to a specified transmission output by a final stage
amplifier, the output power and a reflected wave generated by mismatching between an
output impedance of the final stage
amplifier and a load impedance connected to an output side of the final stage amplifier are detected by a directional coupler. Two switches are selectively switched in a time division manner, a
DC voltage corresponding to the reflected wave is selected, a
comparator compares a
threshold voltage with the
DC voltage, a switch is switched by an output of the
comparator outputted in accordance with the comparison,
and gate voltages are selectively applied to the final stage amplifier.