According an embodiment, a Doherty amplifier includes a carrier amplifier, a peak amplifier, a first line and a second line. The carrier amplifier amplifies a signal and outputs a first output signal. The peak amplifier amplifies the signal and outputs a second output signal. The first line is connected to the carrier amplifier. The second line includes a first end connected to the peak amplifier and a second end connected to the first line. A characteristic impedance of the first end is lower than a characteristic impedance of the second end.