A charged particle beam irradiation system including: an accelerator configured to accelerate charged particles and emit a charged particle beam a stand in which an irradiation section is disposed a transport line which has an energy selection system configured to extract a charged particle beam having a second energy width smaller than a first energy width from a charged particle beam having the first energy width, emitted from the accelerator, and is configured to transport the charged particle beam from the accelerator to the irradiation section and a building having an irradiation chamber and a separate room, wherein the accelerator is disposed in the irradiation chamber, the energy selection system of the transport line is disposed in the separate room, and the building has a partition wall which separates the irradiation chamber and the separate room and is configured to shield against radiation.
