The radiotherapy apparatus in the present invention includes a bed, a radiation irradiating head, head swing mechanisms, a precise inspection unit and a control unit. The bed carries a subject. The radiation irradiating head irradiates a treatment radiation to a treatment field of the subject. The head swing mechanisms, which are coupled to the radiation irradiating head, swings the head of the radiation irradiating head so that the treatment radiation emitted from the radiation irradiating head pursues the motion of the treatment field. The precise inspection unit obtains a diagnosis image containing the treatment field. The control unit controls the positions of the head swing mechanisms so that an irradiation field of the radiation irradiating head pursues the treatment field, based on the diagnosis image, the position of the radiation irradiating head and the state of the swung head. Then, the control unit controls the radiation irradiating head so that the treatment radiation is irradiated from the radiation irradiating head, after the positional control of the head swing mechanisms.