A plurality of transistors operate as amplification elements. An input side coupling circuit comprises a plurality of distributed constant lines connected in series, one terminal of which is an input terminal and the other terminal of which is a bias input terminal. Each of the connection nodes between these distributed constant lines is connected to each of the inputs of the transistors. An output side coupling circuit comprises a plurality of distributed constant lines connected in series, one terminal of which is an output terminal and the other terminal of which is a bias input terminal. Each of the connection nodes between these distributed constant lines is connected to each of the outputs of the transistors. A termination circuit is provided at the input side coupling circuit or the output side coupling circuit. The termination circuit comprises: a first resistor connected between the bias input terminal and a power supply; and a second resistor connected between this bias input terminal and the ground voltage. The resistance value of the first resistor is equal to or less than that of the second resistor.