PURPOSE: To control a pulse width and repetitive oscillation frequency in the wide range and moreover, to accurately make a response at high speed by supplying a control pulse to a switching element connected with a DC power source and controlling its duty factor and repetitive frequency.

CONSTITUTION: Pulses generated by turning on and off the high-speed switching element 2 connected in series with the power source 3 are supplied to an electrode 4 and an object 5 to be worked via a transformer 1 and in the pulse power unit to utilize to work the object 5 to be worked, in a circuit to supply the control pulse via a driver 18 to the high-speed switching element 2, a pulse width modulation circuit is utilized to change and control the oscillation frequency by the output of a working clearance 6 state or state detection circuit 16 of an energizing circuit, by which the pulse width can be controlled in the extremely wide range of ms-μs-ns. The response can be then made at high speed to variation of a working state by controlling the repetitive frequency of the generated pulses by a detection signal of the working clearance 6 state.