Dual-frequency power-supply apparatus, high-frequency heating apparatus, and high-frequency quenching apparatus

A dual-frequency power-supply apparatus comprising:

• a power supply that alternately outputs a first alternating current with a first frequency and a second alternating current with a second frequency higher than the first frequency;
• a first matching box that has a first matching transformer and is capable of receiving an output current of the power supply to output the first alternating current;
• and
• a second matching box that has a second matching transformer and is capable of receiving the output current of the power supply to output the second alternating current,
• wherein the power supply has
• an inverter that converts a direct current into the first alternating current and the second alternating current, and
• a controller that controls the inverter,
• the controller repeats, in this order,
• a first output period in which the first alternating current is output,
• a first intermission in which output is stopped,
• a second output period in which the second alternating current is output, and
• a second intermission in which output is stopped, and
• a length of the first intermission is set longer than a time until a polarity of an output voltage of the power supply is reversed fourthly after transition from the first output period to the first intermission.