A radiotherapy device control apparatus includes: a template matching section; an affected area position calculating section; and an irradiation position control section. The radiotherapy device control apparatus controls a radiotherapy device. The radiotherapy device includes: a therapeutic radiation irradiation device radiating therapeutic radiation, and an imager generating an imager image of a subject by using radiation transmitted through the subject. The template matching section calculates degree of coincidence when a pattern matching is executed on the imager image with a plurality of image templates in which positional relations between an object area and a non-object area of the subject are different, and selects a specified image template having the degree of coincidence within a predetermined range from the plurality of image templates. The affected area position calculating section calculates a position of the object area by using the specified image template. The irradiation position control section judges whether a relative position of the object area with respect to the therapeutic radiation irradiation device. The irradiation position control section moves one of the therapeutic radiation irradiation device and a couch with the subject by using a drive device provided with the radiotherapy device such that the object area is irradiated with the therapeutic radiation.