An amplifier circuit is a cascade amplifier circuit that includes a first transistor circuit including a signal input portion to which a signal is input from outside; a load circuit connected between the first transistor circuit and a power-supply line; and a second transistor cascode-connected between the load circuit and the first transistor circuit. The first transistor circuit is constituted by a plurality of transistors connected in parallel, and a bias circuit is provided that selectively supplies a bias voltage to the plurality of transistors.