Abstract: An electrode holder clamps the electrode 11 in two perpendicular directions by clamp members 33 and 40. Each clamp member slidably rests on base seat 16 which has side portions 17 and 18 that extend at right angles to each other. Clamp screws 60 and 63 along with serrated engaging faces 48 and 54 and engaging members 47 and 53 allow clamp members 33 and 40 to be positioned finely, thereby accurately positioning the electrode 11. Because the respective clamp faces 37 and 44 of the clamp members 33 and 40 are formed to fit each other, even a small-diameter electrode can easily be clamped into position.