PURPOSE: To maximize incident current to a circular accelerator and accumulated current after a multi-turn of incidence in a nondeestructive way, and improve incident efficiency

CONSTITUTION: A beam 11 from a beam transport system is deflected with an incident electromagnet 13 and, then, becomes incident on a circular accelerator. A pickup electrode 12 with a beam passage hole identical to the beam passage hole of the electromagnet 13 or of such a shape as necessary. for the passage of the beam, is laid before the electromagnet 13. Furthermore, a current monitor 14 is laid at a linear section in the accelerator immediately after the electromagnet 13. Also, an output value 15 from the electrode 12 is adjusted to zero or a minimum, thereby transporting maximum beam current up to the electromagnet 13. In addition, while measurements are being taken about an output value 16 from the monitor 14 laid at the linear section within the accelerator immediately after the electromagnet 13, this electromagnet 13 is adjusted to maximize the value 16.