To suppress a harmonic current without adding a component such as a reactor or a capacitor and without changing an output frequency.SOLUTION: A harmonic wave suppression device comprises: a high-frequency power supply device for supplying an AC output power obtained by combining outputs of multiple inverters configured over multiple stages to a resonant load; a PWM signal generation unit 40 for generating a PWM signal of each of the inverters by comparing output command values of the multiple inverters with multiple thresholds that are different from each other; a harmonic wave countermeasure unit 70 for determining a gate width of each of the PWM signals so as to obtain an output voltage width of each of the inverters capable of suppressing a harmonic wave component of the high-frequency power supply device less than or equal to a reference value, on the basis of the output command values and the PWM signals of the PWM signal generation unit 40; and a gate control unit 80 for controlling the switching elements of the inverters in accordance with a gate signal of the gate width that is determined by the harmonic wave countermeasure unit 70.SELECTED DRAWING: Figure 4
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