PURPOSE: To eliminate certainly altering operation of various kinds of restriction bolts so as to simplify sealing structure and operation.

CONSTITUTION: A restriction bolt 1 is screwing fit in a bolt fitting hole 6, and a striking part 7 is provided on the circumferential wall of the restriction bolt 1 or the bolt fitting hole 6. A deformation tool 8 so formed as to be capable of being struck in the striking part 7. Since the restriction bolt 1 is fixed non- rotatably by deformation of the restriction bolt 1 and the like when the deformation tool 8 is struck in the striking part 7, altering operation of the restriction bolt 1 after engine shipment can be prevented certainly. And also it is possible to simplify sealing operation and structure by only striking the deformation tool 8 in the striking part 7.