PURPOSE:To obtain a high accumulated current easily by decreasing the excitation quantity of a six-pole electromagnet or changing the excitation quantity of four-pole electromagnets so that the betatron frequency is separated from the preset value after the incidence start of charged particles. CONSTITUTION:A six-pole electromagnet 11 is installed on the linear section of a circular accelerator, it is excited in advance before charged particles are fed from an inflector 7. On the other hand, focusing and nonfocusing four-pole electromagnets 2, 3 are adjusted in advance so that the horizontal tuning is set near an integer +1/3 or an integer +2/3. The excitation quantity of the six-pole electromagnet 11 is increased or the excitation quantity of the four-pole electromagnets 2, 3 is changed so that the tuning is separated from the preset value after the incidence start of charged particles. A high current can be thereby accumulated easily.