PURPOSE: To make a specific through hole without starvation of cutting fluid unlike in a similar prior-art process for making a through hole, by providing a sealed jig at the other side of a workpiece at which the through hole will open, in order to prevent the outflow of the fluid through the end of the through hole.

CONSTITUTION: An electrolytic hole making system for making a through hole in a workpiece such as a piston head is designed to be slid upwardly and downwardly at a fixed speed along a guide 27 by the power from a motor 26 of a machining electrode driving device 24. A sealed jig 26 is oppositely disposed beneath an electrode 25. Furthermore, this electrolytic hole making device is provided with an electrolyte supply system 30 and a d.c. power source 31. The upper surface of the jig 26 has the identical curved form as the outer side of the inside cylindrical section of the workpiece W. On this upper surface of the jig 26 is fitted a packing which comes in close contact with the outer side of the inside cylindrical section to prevent the outflow of the electrolyte. Accordingly the desired through hole can be produced without electrolyte starvation which, in a prior art, is encountered during hole-making operation.