There is provided a particle-beam energy changing apparatus that is capable of changing energy of a particle beam (1) quickly and silently, in which a first energy changing unit (2) and a second energy changing unit (3) for changing energy of a particle beam (1) passing therethrough by varying thicknesses of their attenuators attenuating the particle beam energy are arranged in such amanner that the particle beam (1) passes through the first energy changing unit (2) and the second energy changing unit (3) and the maximum attenuation amount by the first energy changing unit (2) is set smaller than the maximum attenuation amount by the second energy changing unit (3).
