Abstract: In an output control apparatus for a microwave oven, it is known to insert a control switch in the primary side of a power transformer of a magnetron. In this invention, the control switch is provided in the secondary side of the power transformer either in a magnetron circuit or in a rectifier circuit. The actuation of the control switch is controlled by an on-off control signal such that the control switch is opened and closed respectively within zero-current time periods, of a half-wave current which flows through the rectifier or the magnetron. A transient rush current to the transformer is reduced and reliable intermittent operation of the magnetron is assured.