1. A radiotherapy equipment control device that specifies a position of a specific portion from positions of a plurality of markers in a subject and controls radiotherapy equipment, the radiotherapy equipment control device comprising: a reference position information acquisition unit configured to acquire reference position information representing a position within the body of the subject at a reference time of each of the specific portion and the plurality of markers, using an image captured at the reference time by the radiotherapy equipment; a representative point reference position information computation unit configured to generate reference position information representing a position within the body of the subject at the reference time of a representative point of the plurality of markers from the reference position information of the plurality of markers; a relative position information computation unit configured to generate relative position information of a position represented by the reference position information of the specific portion using a position represented by the reference position information of the representative point as a base point; a marker position information acquisition unit configured to acquire position information of the plurality of markers within the body of the subject at another time different from the reference time, using an image captured at the another time by the radio therapy equipment; a representative point positon information computation unit configured to generate position information of the representative point within the body of the subject at the another time of the plurality of markers from the position information of the plurality of markers; and a specific portion position information computation unit configured to generate position information of the specific portion at the another time from the position information of the representative point and the relative position information, wherein: the radiotherapy equipment is controlled so as to deliver therapeutic radiation to the specific portion using the position information of the specific portion at the another time; the markers are embedded in the vicinity of the specific portion within the subject; the representative point reference position information computation unit specifies a displacement-based or distance-based weight coefficient for each of the plurality of markers and generates the reference position information of the representative point based on the position information of the plurality of markers weighted by the weight coefficient, and the representative point position information computation unit generates the position information of the representative point based on the position information of the plurality of markers weighted by the weight coefficient.