Included are: a first power source 3 configured to output a voltage required for a first gate bias voltage for turning a power amplifier 2 to an ON state; a second power source 4 configured to output a voltage required for a second gate bias voltage for turning the power amplifier 2 to an OFF state; a changeover switch 5 connected between the first power source 3 and the power amplifier 2 and configured to supply either the first gate bias voltage or the second gate bias voltage to the power amplifier 2 by switching a state between the first power source 3 and the power amplifier 2 to either an open state or a short-circuit state on the basis of a control signal related to on-off control of the power amplifier 2; and a resistance value varying unit 15 connected between the second power source 4 and the power amplifier 2 and configured such that a resistance value thereof is variable.