It is better to have compensation slot at the bottom of the piston surrounding ring slot to connect with the compensation hole through the compensation slot.

Provided is a casting mold device capable of keeping constant the clearance between a sleeve inner circumference and a bore pin outer circumference while preventing the drop of a sleeve.

Connection part of the outer peripheral face of edge of the cover section (7, 8) and outer peripheral of the base body (10) constitutes a smooth continuous state without layer difference.