Abstract: An electric discharge machine has a movable ram assembly including a casing having a tubular support defining a through bore therein with an upper portion, a lower portion and a receiving space adjacent to the lower portion. A shaft vertically passes through the bore and the lower end of the shaft is connected to an electrode head. A device for moving the shaft vertically in the tubular support is provided in the casing. The casing also has an upper telescopic member extending upward from the upper portion and a lower telescopic member extending from the lower portion thereof. An insulating device is provided between the shaft and the tubular support to insulate the casing from the shaft. The insulating device includes an insulated tubular member in the lower portion, an insulated sleeve member around the shaft between the upper and lower portions, an insulated stop member at the top end of the shaft.