PURPOSE: To avoid formation of holes on the sinside of a drum or a cylinder by arranging a sharp protrusion to a member for positioning on the side of the cylinder jacket and driving it into the cylinder jacket.

CONSTITUTION: A member 2 is fixed by pressure of springs 2a on the inside of a drum or a cylinder jacket 1. A locating pin 3 having a protrusion 4 is fixed in a hole 5 of the member 2. The protrusion 4 is preferably intruded into the cylinder jacket by 0.25 mm to 2.5 mm. Thereby the time and labor for positioning the member 2 fixedly on the inner surface of the drum or the cylinder jacket are reduced, and the work of forming holes on the drum or the cylinder jacket can be completely eliminated.