The invention relates to an AC-power-fed wire electric discharge machine which can prevent decrease of voltage and improve surface quality and processing precision of workpieces without losing input power energy. The AC-power-fed wire electric discharge machine comprises a power supply portion providing DC power, a converting portion which generates resonance in a resonance circuit according to the prescribed resonant frequency, the resonance circuit which is a serial or parallel circuit for using conductors and capacitors and outputs minimal discharge current under the prescribed resonant frequency, and a magnifying circuit which magnifies the power supply according to predetermined range. DC power fed by the power supply portion is converted into AC power through a conversion circuit, aresonance circuit and a magnifying circuit and the AC power is supplied to the discharge electrodes.