At the start of beam extraction, the amplitude value of an acceleration radio frequency voltage is held at a first amplitude value. When the irradiation dose stemming from beam extraction reaches a prescribed dose, the amplitude value of the acceleration radio frequency voltage applied to an accelerating cavity starts to be increased from the first amplitude value to a second amplitude value. When the irradiation dose reaches a target dose, the amplitude value is raised to and held at the second amplitude value. By the time the irradiation is restarted, the amplitude value of the acceleration radio frequency voltage applied to the accelerating cavity is reduced from the second amplitude value to the first amplitude value. At the start of beam extraction, the amplitude value is held at the first amplitude value.