PURPOSE: To carry out exposure with the luminous intensity of SOR beam being set almost constant in an exposure device using SOR beam.

CONSTITUTION: The intensity of SOR beam 29 is determined with IE3 (I: accmulation current value, E: accumulation energy), wherein the energy E is proportional to the intensity of magnetic field of deflection electromagnet 25. Since electron beam 42 disaperas gradually with the lapse of time, the current value I decreases gradually. Consequently, the excitation amount of deflection electromagnet 25 is increased according to decrease in the value I by detecting the current value I by means of a current monitor 32 and thereby controlling a deflection electromagnet power source 38. In is thus possible to make IE3 almost constant to thereby make the intensity of OR beam almost constant.