After a switching element 13 is turned on, a charge controller 16 determines whether or not a current detected by an excitation current detector 15 has reached a predetermined level, and turns off the switching element 13 if the predetermined level has been reached. When the excitation current is controlled to a constant level, the excitation energy stored in a flyback transformer 12 also becomes constant, and this constant energy is stored in a capacitor 22 every time the switching element 13 is turned off. The charge control section 16 repeats the on/off operation of the switching element 13 a predetermined number of times at predetermined intervals of time before discontinuing the charging operation. Consequently, a constant amount of energy is held in the capacitor 22 when the charging operation is discontinued, and the period of time from the beginning to the completion of charging also becomes constant. Thus, the same conditions are constantly created while the spark discharge is repeated, so that the accuracy and reproducibility of the analysis are enhanced.