A Doherty amplifier includes a first amplifier, a second amplifier, a transmission line, a synthesizer, and an output load. The first amplifier amplifies an RF input signal according to a voltage applied to a supply terminal thereof. The second amplifier amplifies a peak component of the RF input signal according to a voltage applied to a supply terminal thereof. The transmission line is coupled to an output terminal of the first amplifier. The synthesizer is coupled to an output terminal of the transmission line and an output terminal of the second amplifier. It is set such that the voltage applied to the supply terminal of the first amplifier is lower than the voltage applied to the supply terminal of the second amplifier, and that an impedance value of the transmission line is smaller than a value twice an impedance value of the output load.