A microwave signal generator includes a magnetron to generate a microwave signal, a coupler to receive the microwave signal generated by the magnetron and to send the microwave signal to a load; and a band-pass filter to receive the microwave signal from the coupler and to filter the microwave signal to obtain a signal from an oscillation frequency band of the magnetron. The band-pass filter feeds the signal from the oscillation frequency band back to the magnetron in order to fix an oscillation frequency of the magnetron and is a DR (Dielectric Resonator) filter.