1. A radiotherapy equipment control device that specifies a position of a specific portion from positions of a plurality of markers located in the vicinity of the specific portion within 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; 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; a representative point position information computation unit configured to generate position information of the representative point within the body of the subject at the other 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 other time from the position information of the representative point and the relative position information, wherein the representative point reference position information computation unit specifies a 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 wherein 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.