To simply move a shaft by hand so that the shaft can be locked in a desired position, as locking of the shaft in a desired position and changing of a locked position is in convenient in the prior art while preventing the shaft from sliding in its axial center direction.

A tapered ring 3 is inserted slidably in an axial direction into a case main unit 5 covered with a mountable/demountable case cover 6, a friction piece 1 is fitted to a tapered surface 3a formed in an axial center of this tapered ring 3. The friction piece 1 is divided into a plurality of parts radially in an axial center direction from a hole 1a passing through the axial center, a piece spring 2 and a backup spring 4 are arranged respectively between the friction piece 1 and the inside of the case main unit 5 and between the case cover 6 and the tapered ring 3, elastic force of the latter is set larger than elastic force of the former, a shaft 7 is inserted through the case cover 6, case main unit 5 and the hole 1a of the friction piece 1, a ring part 6a is protruded inside the case cover 6, and a clearance 1 is formed between the friction piece 1 and the shaft.