An embodiment of the present invention provides a radiation therapy device including: a main body； a gantry coupled to a side of the main part and rotatable relative to the main part in at least one direction； a radiation head provided on a side of the gantry to emit radiation； an image acquisition unit facing the radiation head to detect radiation emitted from the radiation head and obtain images by converting the detected radiation into electric signals； and a reference image acquisition frame provided on a side of the radiation head and including a plurality of markers formed thereon.
