To improve an efficiency of utilizing electrons and efficiently suppress an ion beam spread by a space charge effect while eliminating a need for a special magnetic pole structure by effectively using a space in the vicinity of a magnet, there are provided an ion source, a collimating magnet and a plurality of electron sources, wherein the electron sources are arranged in a magnetic field gradient region formed on an ion beam upstream side or ion beam downstream side of the collimating magnet and arranged outside a region passed by the ion beam, and an irradiation direction of the electrons is directed to supply the electrons to the magnetic field gradient region.