A microwave heating cooker (1) includes a high-frequency power source (10). The high-frequency power source (10) includes a first semiconductor amplification circuit (amplifier) (3), a second semiconductor amplification circuit (amplifier) (4), an antenna (power supply unit) (5), a high-frequency generation unit (6), a commercial power source (alternating current power source) (7), a first full-wave rectification circuit (11), and a switching converter (12). The high-frequency generation unit (6) is configured from a commercial transformer (20), a second full-wave rectification circuit (21), resistors (22 and 23), an amplifier (24), an analog multiplier (amplitude modulation unit) (25), and a high-frequency oscillator (oscillator) (26), among others. The analog multiplier (25) modulates the amplitude of the output voltage from the high-frequency oscillator (26) with a signal wave that is in synchronism with a half-period of the cycle of the commercial power source (7).