A power amplifier includes: an amplifier having a base into which input signals are input, a collector to which a collector voltage is supplied, and an emitter; and a bias circuit for supplying a bias current to the base of the amplifier. The bias circuit includes a first transistor having a first control terminal into which a reference voltage is input, a first terminal to which a power voltage is applied, and a second terminal connected to the base of the amplifier. A capacitance adjusting circuit elevates capacitance between a grounding point and at least one of the first control terminal and the first terminal when the collector voltage of the amplifier is lowered.