Abstract: Provided is a collimator device for radiotherapy including: a body including a first through unit and disposed on a path of high energy radiation which in use is irradiated toward a patient's treatment part; a frame including a through hole corresponding to the first through unit and slidably installed in the body; a plurality of multi-leaf collimators (MLCs) slidably installed in the through hole and including radiation shields; a servo motor coupled to the body and the frame in a power manner so as to slidingly move the frame with respect to the body; and a motor controller externally receiving position displacement data regarding a motion of the patient's treatment part due to a patient's breathing and generating a signal for controlling the driving of the servo motor so that the MLCs follow the patient's treatment part and continuously apply radiation to the patient's treatment part based on the position displacement data.