A power amplifier includes: an amplifying transistor; a bias circuit; a first diode; a second diode; a matching attenuating circuit; a first current mirror circuit; a serial resonant circuit, and a switch. In an amplification mode, the bias circuit supplies a bias current to the amplifying transistor, and the first current mirror circuit turns off the first and second diodes, and the switch. In an attenuation mode, the bias circuit supplies no bias current to the amplifying transistor, and the first current mirror circuit turns on the first and second diodes, and the switch.