A high-frequency power circuit includes a first antenna circuit and a second antenna circuit that are connected in parallel to a matching box connected to a high-frequency power supply. The first antenna circuit include a first antenna, a first distribution capacitor, and a first variable capacitor. The second antenna circuit includes a second antenna, a second distribution capacitor, and a second variable capacitor. A controller sets a capacitance of the first variable capacitor based on a detection result of a phase difference between current and voltage in a series-connected portion of the first antenna and the first variable capacitor during plasma production to reduce this phase difference and sets a capacitance of the second variable capacitor based on a detection result of a phase difference between current and voltage in a series-connected portion of the second antenna and the second variable capacitor during plasma production to reduce this phase difference.