Abstract: An apparatus for controlling an oscillation output of a magnetron includes a switch circuit controlled of ON/OFF states thereof by a pulse signal, a rectifying circuit for supplying microwave power pulses to the magnetron, and a transformer having a primary side and a secondary side. The primary side has a first terminal and a second terminal, where the first terminal is connected to an A.C. power supply, the second terminal is connected to the switch circuit. The secondary side is connected to the rectifying circuit. The switch circuit is turned ON/OFF by the pulse signal so that a duty factor of the microwave power pulses output from the rectifying circuit and a repetition frequency of the duty cycle thereof become constant.