PURPOSE: To accurately hold electrodes and enable the electrode to easily perform simultaneous machining, by holding the electric discharge machining electrode to a plurality of threaded holes drilled lining in a predetermined space on plural surfaces of a squared block and providing a mounting part to an electric discharge machine on at least one of the plural surfaces.

CONSTITUTION: A squared block 10 holds on its each surface an electrode to be mounted by a thread. And an electric discharge machine mounting part 15, provided on one surface of the block 10, provides a crossed V-groove 15a to be engraved. An electric discharge machine connects with its main spindle 17 a male coupling 16, and the coupling 16 fits its four V-shaped protrusive parts 16a to the grooves 15a while fits a tightening part 16b to be inserted into an engaging hole in the center. Under the condition, if an eccentric pin 18, being inserted into a stop hole 16d at a right angle with the axial direction of the tightening part 16b and a through hole of the squared block 10, is turned together, the squared block, being brought in a direction of the coupling 16 by the cam action of the pin 18, is connected with the male coupling 16. And the block, in which the groove 15a is connected with the protrusive part 16a by each tilt surface being brought into contact with each other, obtains the correct center, plane and the phase.