An output mode switching amplifier, including: a transistor for signal amplification connected between a first node on an input side and a second node on an output side; a bypass path for bypassing the transistor between the first node and the second node; a voltage control circuit for switching whether to apply a bias voltage to the transistor so that a transmission signal is amplified by the transistor or to output a transmission signal via the bypass path without amplifying the transmission signal by the transistor; and a second-harmonic reflection circuit connected to the bypass path, for reflecting a second harmonic of the transmission signal.