An amplifier according to an embodiment of the present disclosure includes a first transistor and a first matching circuit. The first matching circuit is connected between an input terminal and a control terminal of the first transistor. A first terminal of the first transistor is connected to a ground. A second terminal of the first transistor is connected to a power supply and an output terminal. The first matching circuit includes a first inductor, a second inductor, and a first switch. The first inductor has an end connected to the control terminal. The second inductor has an end connected to the other end of the first inductor. The first switch is configured to selectively switch between electrical continuity between the input terminal and the other end of the first inductor and electrical continuity between the input terminal and the other end of the second inductor.