PURPOSE: To prevent rotation of a pin without using a jig by constituting the pin out of a pin member in which thread is formed on one end and the inner wall of the groove of a first cylindrical member is formed to obstruct the rotation, and a screw member threadedly engaging with the thread of the pin member through the through hole of the first cylindrical member from the circumferential face on the opposite side to the circumferential face arranged with the pin member.

CONSTITUTION: In the construction of a roller shaft 13 for a first group, a flange part 13a of a shape in which a disc plate is cut out from both sides in parallel is provided on the extreme end of a columnar shaft part 13b, and female thread hole 13c along the axis is provided on the base end face. Under the condition in which the shaft part 13b is inserted through a roller 14 for a first group, they are inserted into a moving frame 7 for a first group as a first cylindrical member fitted to the outer circumference of a cam ring 6 from the inside of a rectilinear guide ring 5. At this time, the cutout part of the flange part 13a of the roller shaft 13 is put in parallel with a rectilinear guide groove 5a. A set screw 16 of screw member of larger diameter head than a roller fitting hole 7a is screwed in the screw hole 13c of the roller shaft 13 from the outside of the moving frame 7.