The upper electrode 31 has a hole 35 extending from an upper surface 33 to a lower surface 34, a bolt 36 is inserted from the upper surface 33 of the upper electrode 31 into the hole 35, and secured in a lower electrode 32 by a screw. A gap 51 between an inside of the hole 35 and a straight body portion of the bolt 36 allows the upper electrode 31 to slide in all directions in a placement surface (upper surface of the lower electrode 32 in contact with the lower surface 34 of the upper electrode 31 in FIG. 2) that is a contact surface with an upper surface of the lower electrode 32, thereby providing an effect of preventing occurrence of a crack or a break in a U rod that can be expanded and contracted in all directions during a vapor phase growth process.