In a magnetron drive apparatus, a high frequency voltage converted and outputted by a frequency converter is inputted to a primary winding (52a) of a transformer (52) and a high voltage power outputted from a secondary winding (52b) of the transformer (52) is rectified and supplied to an anode of the magnetron and a power outputted from a heater winding (52c) of the transformer is supplied to a heater of the magnetron. The magnetron drive apparatus comprises a magnetic flux leakage device (AG) disposed in a magnetic path formed by the primary and secondary windings (52a, 52b) of the transformer (52) and increasing a leakage magnetic flux in the magnetic path; and a device (52g) for winding the secondary winding (52b) and the heater winding (52c) therearound in a position opposite the primary winding (52a) with the magnetic flux leakage device (AG) arranged therebetween.