An electric power unit for machining of a wire electric discharge machine for machining a workpiece (W) in which an electric discharge inductive pulse voltage is impressed upon between electrodes of a wire electrode (E) and workpiece (W), after insulation between the electrodes has been broken by the pulse voltage and electric discharge has been induced, a pulse voltage for machining is impressed upon between the electrodes so as to conduct machining on the workpiece (W). The electric power unit for machining of a wire electric discharge machine includes an electric discharge state discriminating means (1a) for discriminating a state of electric discharge generated between the electrodes and an impression voltage selecting means (1b) for inverting the polarity of the electric discharge inductive pulse voltage from the previous electric discharge inductive pulse voltage when an electric discharge state between the electrodes is discriminated to be abnormal (Y1) or open (Y3) by the electric discharge state discriminating means (1a) and for making the polarity of the electric discharge inductive pulse voltage to be the same as the polarity of the previous electric discharge inductive pulse voltage when the electric discharge state between the electrodes is discriminated to be normal (Y2) by the electric discharge state discriminating means. Thus the machining efficiency is improved.