PURPOSE: To enable irradiating radiation at one point with a high position accuracy by using a means for electrically controlling an electron beam for controlling the radiation irradiation direction distributing the radiation generation points three dimensionally and irradiating from an arbitrary directions at a microspot.

CONSTITUTION: An accelerated 1 electron beam 2 is converged with 4 electropole lens 3 and irradiate a target 5 by receiving reversed bias by a bias meters 4-1 and 4-2. The target 5 radiates radiation 6 and the radiation 6 is colimated 7 so as to irradiate a microspot 8 in the head of a patient. Here the beam 2 is scanned in turn from the targets 5-1 to 5-9 corresponding to the colimeter 7-1 to 7-9. This is done by changing the bias intensity of bias meters 4-1 to 4-2. At this moment, the lens 3 is synchronized to strengthen the lens intensity and the beam 2 is converged thin on the target 5. The bias meters 4-1 and 4-2 and the target 5 rotate altogether therefore, the radiation can be irradiated to a microspot 8 from three dimensionally different angle.