Radiation therapy equipment includes a multi-divided irradiation collimator leaf plates for setting irradiation field as approximately close to a target region as possible by avoiding backlashes due to a plurality of gears for driving a plurality of leaf plates. The plurality of leaf plates is respectively connected to a plurality of constant force springs that are coaxially supported by a pair of rotation shafts so as to be constantly forced in a closing direction. Each leaf plate is moved in an opening direction by rolling up a wire connected to the leaf plate.