PURPOSE: To make automation for the setting and changing of an electrode and unmanned automatic operation performable, by installing an electrode signal memory, an electrode changer and a numerical control system setting a working condition on the basis of an electrode signal corresponding to the changed service electrode.

CONSTITUTION: An electrode changer 2 takes a corresponding service electrode 6 out of a magazine by a program signal to be inputted out of a ketboard and a table reader or the like and attaches it to an electrode holder 7. And, the working fluid pressure related to material and size of the electrode 6 and material and thickness of a workpiece 13 and the table that stored an electric condition both are stored in a read-only memory of a numerical control system 34, whereby the working fluid pressure and the electric condition are read by an electrode signal of a program being inputted out of the keyboard and the tale reader or the like, and the NC system 34 controls a feed pump driving motor 18 and a pressure regulating motor 22 so as to become the working fluid, while it selectively sets output of a working power source, namely, on-off time, dwell time or the like according to the read electric condition, thus optimum machining is made so as to be done.