PURPOSE: To realize the switching of a microwave large in power, by separating a transmission line between an input port and an output port to a distributor and a synthetic system of the distributor and a synthesizer by the distributor, setting the least significant branch transmission line as a strip line, and providing an impedance variable device on it.

CONSTITUTION: The transmission line 10a including the input port 10 is branched to the strip lines 12a, 12b, 13a, and 13b by bisected distributors 11, 12, and 13, and next, each strip line is synthesized to the transmission line 16a including the output port 17 by the synthesizers 14, 15, and 16. FETs 18, 19, 20, and 21 as the impedance variable devices are connected to each strip line, and by impressing a negative voltage on gate voltage controlled terminals 22a and 22b, impedance between the drain and the source of each FET is increased, and the microwave on each strip line passes as it is, and by impressing 0V, the impedance is decreased, then, a reflected wave is generated at a connection point P on each strip line, and a small power is outputted to the output port 17.