1. A particle beam therapeutic apparatus in which a flow of a particle beam transported so as to be irradiated to a diseased part is caused to deflect in two mutually orthogonal directions perpendicular to the direction of travel of said particle beam, and the irradiation position of said particle beam is scanned, upon each period, in a manner to return to a position of irradiation located at the start of said period, whereby a plurality of loci drawn within one period are overlapped with one another thereby to irradiate a desired planned dose to said diseased part, wherein said particle beam can be interrupted only at the end of said period.