PURPOSE: To obtain the high frequency amplifier capable of more reducing power consumption than that at present and attaining high efficiency.

CONSTITUTION: The high frequency amplifier amplifying a high frequency signal coming to an input terminal 1 and supplying high frequency power to a load connecting to an amplifier 2 is provided with a detection means 4 giving an output in response to a high frequency signal and with a switching means 5 switching the power supply circuit connecting to the amplifier 2 in response to the output of the detection means 4.