PURPOSE: To lessen the scatter of discharge energy even against the change of a machining gap, by an electric source apparatus for cutting a wire with an electric discharge, the apparatus including a combination of a voltage variable direct current power source, a high direct current power source, and main and subsidiary switch circuits.

CONSTITUTION: When the output S3 of a discriminator 44 and the output S1 of an oscillator 32 are given to a delay-differentiating circuit, the output S4 of an AND gate 36 triggers and drives a vibrator 38. The output S5 thereof drives to close a main switching circuit 30. After a sub-switching circuit 28 becomes conductive to energize the machining gap with an electric voltage E1, and a certain delay time has passed, the main switching circuit 30 is set to close or open according as an electric discharge has been generated or not. If a normal electric discharge is generated by the energized voltage E1 from the first direct current power source 26, the discharge can be succeeded even if the second direct current power source 26 has a high output voltage and a high peak current capacity.