To form a device easily and enable it to be repetitively used by allowing bars that constitute layers and are located in parallel with each other to come into and go from a region, where a charged particle beam passes through, by separate movement of the bars.

First of all, a tumor 25 is divided into lamellar regions of a prescribed thickness and a magnetic field is set up so that central plane of the first lamellar region can be irradiated with a charged particle beam 18. Then, the track of the particle beam 18 is approximately matched with the shape of an inner-side boundary surface of the first lamellar region by moving a bar 19b of an energy compensator 19. Moreover, an irradiation range is restricted within the lamellar regions by regulating a collimator 22. In this state, the central plane of the first lamellar region is irradiated with the particle beam 18 deflected by an electromagnet 16 for deflection in the X direction, and a particle beam 15 is turned off when the number of irradiated particles reaches a prescribed value. Subsequently, only a prescribed amount of the particle beam 18 in the number of particles is radiated by increasing the thickness of an energy shifter 21 by a prescribed amount. Thereafter, such processes are repeated and the irradiation is completed.