PURPOSE: To easily change the dosage of an electron beam to desired dosage by positioning metallic foil with desired thickness and an electron beam passing part to the locus route of electron corresponding to electron dosage required for treatment.

CONSTITUTION: The electron discharged from an electron gun is accelerated sequentially at every passage of acceleration cavity 13 in an accelerator 11, and also, passes a start-up route 12 opened gradually sequentially. At this time, the electron is abutted with the metallic foil 16a-16n of a rotary frame 18 positioned at the route 12 when it passes the metallic foil, and is scattered, whidh reduces the dosage. Thence, it passes a gantry 14, and is projected on the faulty part of a body to be inspected via a dosimeter 15. At this time, a dosage control circuit 24 drives a motor 19 and rotates the rotary frame 18 via a driving control circuit 23 corresponding to irradiation dosage by the detection of the dosimeter 15, and positions the metallic foil with desired thickness out of the metallic foil 16a-16n at the route 12, and controls the irradiation dosage.