A radiotherapy apparatus controller, comprising: a planning-stage position data collecting section configured to collect planning-stage position data which indicates a planning-stage position where a subject is lying on a couch during a planning stage, the couch being driven by a couch driving device which is controlled by the radiotherapy controller; a position-adjusting-stage position data collecting section configured to measure position-adjusting-stage 3-dimensional data which indicates a position-adjusting-stage position where the subject is arranged during a position-adjusting stage different from the planning stage; a correction amount calculating section configured to calculate a treatment-stage position, a gantry-angle offset value and a ring-angle offset value based on the planning-stage position data and the position-adjusting-stage 3-dimensional data; a treatment plan collecting section configured to collect an irradiation direction in which an irradiation head is arranged with respect to the planning-stage position, the irradiation head being supported by a gantry, the gantry being supported rotatably with respect to a ring, and the ring being supported rotatably with respect to a base; and an irradiation head driving section configured to control an irradiation head driving device, which moves the ring and the gantry, based on the irradiation direction such that the ring is arranged at a corrected ring angle with respect to the base and the gantry is arranged at a corrected gantry angle with respect to the ring; wherein the irradiation direction indicates a gantry angle and a ring angle; the corrected ring angle indicates the difference that the ring-angle offset value is subtracted from the ring angle; the corrected gantry angle indicates the difference that the gantry-angle offset value is subtracted from the gantry angle; the gantry-angle offset value and the ring-angle offset value are calculated such that the irradiation head is arranged in the irradiation direction with respect to the treatment-stage position when the ring is arranged at the corrected ring angle with respect to the base and the gantry is arranged at the corrected gantry angle with respect to the ring; and the movement of the subject from the position-adjusting-stage position to the treatment-stage position is formed of a rotational movement rotating around a rotational axis parallel to a direction fixed with respect to the base and a parallel movement with respect to the base. a planning-stage position data collecting section configured to collect planning-stage position data which indicates a planning-stage position where a subject is lying on a couch during a planning stage, the couch being driven by a couch driving device which is controlled by the radiotherapy controller; a position-adjusting-stage position data collecting section configured to measure position-adjusting-stage 3-dimensional data which indicates a position-adjusting-stage position where the subject is arranged during a position-adjusting stage different from the planning stage; a correction amount calculating section configured to calculate a treatment-stage position, a gantry-angle offset value and a ring-angle offset value based on the planning-stage position data and the position-adjusting-stage 3-dimensional data; a treatment plan collecting section configured to collect an irradiation direction in which an irradiation head is arranged with respect to the planning-stage position, the irradiation head being supported by a gantry, the gantry being supported rotatably with respect to a ring, and the ring being supported rotatably with respect to a base; and an irradiation head driving section configured to control an irradiation head driving device, which moves the ring and the gantry, based on the irradiation direction such that the ring is arranged at a corrected ring angle with respect to the base and the gantry is arranged at a corrected gantry angle with respect to the ring; wherein the irradiation direction indicates a gantry angle and a ring angle; the corrected ring angle indicates the difference that the ring-angle offset value is subtracted from the ring angle; the corrected gantry angle indicates the difference that the gantry-angle offset value is subtracted from the gantry angle; the gantry-angle offset value and the ring-angle offset value are calculated such that the irradiation head is arranged in the irradiation direction with respect to the treatment-stage position when the ring is arranged at the corrected ring angle with respect to the base and the gantry is arranged at the corrected gantry angle with respect to the ring; and the movement of the subject from the position-adjusting-stage position to the treatment-stage position is formed of a rotational movement rotating around a rotational axis parallel to a direction fixed with respect to the base and a parallel movement with respect to the base.