A power amplifier comprises: an amplifier transistor; a bias circuit supplying bias current to the amplifier transistor; and a collector voltage terminal connected to a collector of the amplifier transistor. The bias circuit includes: a reference voltage terminal into which a reference voltage is input; a power terminal connected to a power source; a transistor having a control terminal connected to the reference voltage terminal, a first terminal connected to the power terminal, and a second terminal that is grounded. The transistor supplies a bias current corresponding to the reference voltage to the amplifier transistor; a variable capacitor connected between the first terminal and a grounding point; and a logic circuit controlling capacitance of the variable capacitor.