Provided are a magnetron-driving power supply and a high-frequency heating device equipped with the same, such that the power supply can operate with a high power factor without being affected by variations in the type or characteristics of the magnetron. A voltage from an alternating current power supply (20) is rectified; one of input voltage waveform information (92) and input current waveform information (91) of an inverter circuit which conducts high-frequency switching to transmit electric power is selected, wherein the one having a greater amplitude than the other is selected; the selected one of input voltage waveform information (92) and input current waveform information (91) is superimposed on electric power control information (93) by a mixing circuit (73) to pulse-width modulate the switching of a switching transistor (37); and the signal amplitude is changed between start-up control and steady-state control. In this way, the pulse-width modulation control pattern for each of the start-up control and the steady-state control can be optimally designed according to respective control requirements, and therefore, more stable control of the magnetron-driving power supply can be achieved.
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