PURPOSE: To permit dealing with the magnitude of processing energy without changing a transistor element from a processing region where processing energy is needed to be reduced to a processing region where the processing energy is required to be increased by mutually parallelly connecting plural electrostatic induction transistors for generating pulse voltage.

CONSTITUTION: A power source for electric discharge processing has, for example, an A.C. source 1 for three-phase A.C. 200 V, a rectification part 2 connected to the A.C. source 1 and rectifying A.C. to D.C., a pulse conversion part 3 converting a D.C. current rectified in the rectification part 2 to a pulse wave having desired pulse width and pulse voltage, and a transistor drive part 5 which is composed of e.g. five drive circuits 4... parallelly connected and in which the input sides of these drive circuits 4... are individually connected to the output side of the pulse conversion part 3. Moreover a pulse voltage applying part 7, having electrostatic induction transistors 6 individually connected to the output side of the drive circuits 4..., is provided, and pulse voltage is freely adjusted corresponding to the magnitude of processing energy.