An amplifier transistor operates in two operation modes having different characteristics. A first bias circuit including a first bias supply transistor supplies an output current of the first bias supply transistor to the amplifier transistor as a bias current. A second bias circuit including a second bias supply transistor supplies a portion of an output current of the second bias supply transistor to the amplifier transistor as a bias current. At least one of the first bias circuit and the second bias circuit is selected and operates in accordance with an operation mode of the amplifier transistor by using a bias control signal input to a bias control terminal. The second bias circuit includes a current path along which a portion of the output current of the second bias supply transistor is returned to the second bias circuit.