PURPOSE: To attain aging of a load with a simulated load by providing a coaxial switch switching a load and the simulated load and a coaxial connector connecting and disconnecting a circulator and the simulated load and operating the coaxial switch and the coaxial connector.

CONSTITUTION: Minute high frequency power of an oscillator 1 is amplified into large power by an amplifier 2 and when the large power is supplied to a load 7 through a circulator 3, the coaxial switch is thrown to the position (a). When the output test of a high frequency power is conducted without the load 7 or with the load 7 no power applied thereto, the coaxial connector 8 is disconnected and the coaxial switch 4 is thrown to the position (b). Thus, one simulated load 5 is enough for the purpose. Thus, a small sized economical acceleration high frequency power supply is formed.