Abstract: Provided is a technique by which each nuclide is optimized in terms of energy and number of particles and pre-accelerated so as to be injected into a main accelerator in charged particle beam irradiation by the combined use of different nuclides. A charged particle beam injector includes: a first ion source that generates first nuclide ions; a first linear accelerator that linearly accelerates the generated first nuclide ions to form a first charged particle beam; a second ion source that generates second nuclide ions; a second linear accelerator that linearly accelerates the generated second nuclide ions to form a second charged particle beam; and a switching electromagnet that injects one of the first charged particle beam and the second charged particle beam into an inflector of a main accelerator.