To provide a microwave generator capable of precisely controlling filament temperature of a magnetron for realizing long service life of the magnetron.

This microwave generator is provided with the magnetron 74 wherein a negative electrode 80 comprising a filament 78 and a positive electrode 82 comprising a cavity resonator 84 are arranged facing each other and which generates a microwave by oscillating when provided with a magnetic field, a filament power supply 98 supplying adjustable power to the filament, a filament current measuring part 100, a voltage measuring part 102 measuring the voltage applied to the filament, a resistance value calculation part 104 calculating a resistance value of the filament based on the measured current and voltage, a temperature calculation part 106 calculating the temperature of the filament based on the calculated resistance value and resistance-temperature dependence characteristics of the filament obtained in advance, and a power supply control part 110 controlling a filament power supply so that the temperature of the filament is kept within a prescribed temperature range.