Abstract: A DC power source constituted by a power generator (20), a dynamo (22) and a rectification means (23), an inverter power source (24) which boosts an output of the DC power source so as to drive a magnetron (28) and an inverter controller for controlling the inverter power source (24) by an output of a generated electric power output detecting means (31) for detecting the output of the DC power source are provided, whereby a required dielectric heating function can be stably achieved by controlling an operational state of the inverter power source (24) by the output of the DC power source.