PURPOSE: To reduce an insertion loss and to improve an isolation characteristic in a high frequency switching circuit for turning on/off a microwave band or milliwave band signal.

CONSTITUTION: The high frequency switching circuit is provided with a 1st amplifier 4 for amplifying a modulation signal having a fo/n frequency outputted from a modulator 5, a multiplier 1 for multiplying the modulation signal having the fo/n frequency by (n) to obtain a modulation signal having the fo frequency, a 2nd amplifier 2 for amplifying the modulation signal having the fo frequency and applying the modulated signal to an antenna 6, and a control part 3 for controlling the operation point of the multiplier 1 and the operation power supply voltage of the 1st and 2nd amplifiers 4, 2 to control the ON/OFF of the modulation signal having the fo frequency to be applied to the antenna 6.