Radiotherapy device comprising a positioning device, and positioning method

A positioning device that controls a position of a treatment-couch on which a subject is mounted, the positioning device comprising:

• an image acquisition part that acquires a plurality of fluoroscopic images obtained by imaging the subject by detecting, on a detection surface via the subject, light from a light source for each of a plurality of imaging axes;
• a creation part that creates, for each of the plurality of imaging axes, a simulated fluoroscopic image obtained by projecting a three-dimensional fluoroscopic image of the subject onto the detection surface with respect to each imaging axis of the plurality of imaging axes;
• and
• a calculation processing part that obtains, for each of the plurality of imaging axes, a correction axis obtained by correcting each imaging axis of the plurality of imaging axes based on a deviation amount between a fluoroscopic image of the plurality of fluoroscopic images and the simulated fluoroscopic image corresponding to each imaging axis of the plurality of imaging axes, and calculates, as a treatment-couch motion amount by which the treatment-couch is to be moved, a motion amount from an intersection of the plurality of imaging axes to a midpoint of a common perpendicular of correction axes.