PURPOSE: To improve a speed of processing as well as accuracy of processing by providing many pores or drilled holes in an electrode, and allowing any gas or fluid to exude in part onto a surface of the electrode.

CONSTITUTION: An electrode 1 comprising a porous metal sintered body and an expansion molded body has many pores 1a and is connected with a gas/fluid supply pipe via a void 2. N2 gas is supplied from the gas supply pipe, while a solution of hydrocarbon is supplied from the fluid supply pipe, and they are changed over by means of a valve with the aid of a control device. Electric discharge is produced among respective positions of the electrode or interrupted by the changeover to the supply pipe, whereby discharge points are moved. Arc discharge is stopped by exudation of N2 gas, and the discharge points are moved to another portions for effecting stable processing.