PURPOSE:To make discharge energies uniform, by detecting a current value or a variation rate thereof at an arbitrary time from the time when a large current pulse is started to run upon initiation of electric discharge, to turn on and off a main d.c. current source thereby the pulse width is controlled. CONSTITUTION:The output of a current detector 10 for detecting discharge current is delivered through a differential amplifier 18 to a discharge start detecting circuit 23 and to comparators 19a through 19n. The circuit 23 detects a current from a discharge capacitor and delivers its output signal to a pulse oscillating circuit 24 so that a control signal S3 for a switching element is issued. Further, a timing pulse generating circuit 20 receives the signal S3, and issues a pulse to gate circuits 21a through 21n so that it is detected in which range the value that is obtained after a predetermined time elapsed from the time when a large current is started to run, exists between comparator reference voltages E1 through En. Accordingly, the associated gate is opened, and pulse data are taken out from the associated address in a memory 22 and are delivered to the pulse oscillating circuit 24. Thus, discharge energies from pulses are ideally made substantially uniform.
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