In an electric discharge machining apparatus that machines a workpiece (1) by using a water-based dielectric fluid as a dielectric fluid while a voltage is being applied to a machining gap between an electrode (2) and the workpiece (1), the electric discharge machine includes:an anticorrosive power source section (26) that applies a predetermined voltage by taking the workpiece (1) as a cathode and taking as an anode an anticorrosive electrode (25) opposing the workpiece (1) with an insulator (24) therebetween;a dielectric fluid quality measuring instrument (22) that measures a quality of the dielectric fluid; anda dielectric fluid quality control section (16, 17, 18, 19, 20, 21, 23) that controls a pH level of the dielectric fluid to be within a range from 8.5 to 10.5 on the basis of the measured result of the dielectric fluid quality measuring instrument (22).