PURPOSE: To prevent the discharge of a rocket or a satellite or the like and to simplify the procedure when a high power RF signal is switched in a pressure zone in which the rocket or satellite is easily discharged.

CONSTITUTION: A voltage is applied to a base of a transistor(TR) 5 only when a command signal S is inputted between terminals (A) and (C) or between terminals (B) and (C) of a coaxial switch 1, an RF signal is fed to a circulator 2, a capacitor 3 and the TR 5 to a resistor 6 to interrupt the input to the coaxial switch 1. On the other hand, the changeover of the coaxial switch 1 switch 1 is finished in a time when the command signal S is applied thereto. Since no RF high power is applied to the coaxial switch 1 during the changeover operation, it is not possible to damage the coaxial switch 1 and not required to interrupt the RF signal at the changeover.