An energy amount control device having a pulse energy generating source which produces pulse energy with a predetermined range of energy fluctuations per oscillation, and adjusting voltage applied to the energy generating source to thereby control an energy amount of the pulse energy, the energy amount control device comprising a storage unit for storing information about the relation between predetermined voltage to produce pulse energy in the energy generating source and an energy amount of the pulse energy emitted from the energy generating source under the predetermined voltage; an energy amount measuring unit for detecting the energy amount of the pulse energy actually emitted from the energy generating source; an arithmetic unit for updating the information stored in the storage unit at predetermined timing based on the predetermined voltage to produce the pulse energy in the energy generating source and the energy amount detected by the energy amount measuring unit; and decision unit for determining the predetermined voltage corresponding to the energy amount of the pulse energy to be next emitted, based on the information updated by the arithmetic unit.