A high-frequency power apparatus including: an oscillator, outputting an oscillating signal, an output level of the oscillating signal being variable; an amplifier, amplifying the oscillating signal output from the oscillator and outputting high-frequency power; a DC power supply, supplying DC power to the amplifier, an output level of the DC power being variable; a high-frequency power measuring unit, measuring a power value of the high-frequency power at an output terminal of the high-frequency power apparatus and outputting the measured power value as a high-frequency power measured value; a DC power measuring unit, measuring a power value of the DC power supplied to the amplifier and outputting the measured DC power value as a DC power measured value; a first controller, controlling the output level of the oscillating signal to be output from the oscillator such that the high-frequency power measured value is substantially equal to an output power set value; and a second controller, controlling the output level of the DC power to be supplied from the DC power supply to the amplifier such that a calculated value obtained by dividing the high-frequency power measured value by the DC power measured value is substantially equal to a predetermined efficiency set value.