A synchrotron injector system comprising a first ion source (1) which generates first ions, a second ion source (2) which generates second ions having a smaller charge-to-mass ratio than a charge-to-mass ratio of the first ions, a pre-accelerator (5) having the capability to enable to accelerate both the first ions and the second ions, a low-energy beam transport line (4) which is constituted in such a way to inject either the first ions or the second ions into the pre-accelerator, and a self-focusing type post-accelerator (6) which accelerates only the first ions after acceleration which are emitted from the pre-accelerator (5).
