PURPOSE: To surely prevent cooling liquid from leaking to outside even if a pin hole is generated on a spacer by constituting packing with plural annular thick parts and plural annular thin parts connecting the thick parts.

CONSTITUTION: A 1st packing 6 consists of a 1st thick part 6a whose respective cross-sectional shapes are rectangular, a 2nd circular thick part 6b, plural circular 3rd thick parts 6c having a diameter smaller than that of the thick part 6b and arranged between both the thick parts 6 a, 6b and plural thin parts 6d connecting these thick parts. A 2nd packing 7 is also constituted of a 1st thick part 7a, a end thick part 7b, plural 3rd thick parts 7c, and plural thin parts 7d. Since these packing members 6, 7 are used, plural 3rd parts can prevent the cooling liquid rom leaking to outside even if a pin hole is generated on the spacer 2 in the casting process.