An energy degrader includes a plurality of attenuating members configured to attenuate the energy of an incident charged particle beam, the plurality of attenuating members having different amounts of energy to be attenuated. A low-energy-side attenuating member that is the attenuating member with a larger amount of energy to be attenuated is made of a material having a higher transmittance of the charged particle beam than that of a high-energy-side attenuating member that is the attenuating member with a smaller amount of energy to be attenuated.
