PURPOSE: To detect it by a user at a glance that a clutch disc is brought into a wear limit by providing a support part having an engaging claw disposed to a cylinder body and a pointer scale having an engaging part engaged with the engaging claw and slidable.

CONSTITUTION: In a cylinder body 11, a support part 30 having an engaging claw 30a is fixed to a mounting part 20 through mutual fastening and a pointer scale 31 is engaged with the engaging claw 30a. The pointer scale 31 is formed of resin and an engaging part 31a engaged with the engaging claw 30a is formed in a corrugated shape. Further, the pointer scale 31 is slidable over the support part 30 and easily set to an arbitrary position. In initial setting, a position when a clutch disc is brought into a wear limit is predetermined. The pointer scale 31 is set in such a manner that the clutch disc reaches a wear limit when a release folk 17 is brought into contact with the end part of the pointer scale 31. This constitution detects it by a user at a glance that it reaches a wear limit.