To provide a pulley that permanently supports an extremely high force in a pressure chamber and maintains a preferable characteristic of hinging.

A set of pulleys is disposed in a transmission 1, at least one disk can move in the axial line direction, the disk has a cylinder/piston means 12, the cylinder/piston means 12 has at least one pressure chamber 13 having radial walls and concentric cylinder walls, at least one of the radial walls 18 and 24 of the pressure chamber is fixed to one 20 of the concentric cylinder walls by fixed engagement, and the wall 18 near the engagement is formed so as to have an elastic hinge shape. The shape of the hinge is formed so as to have a sleeve-like boss part 30 extending in the axial direction, the boss part 30 is integrated with the wall 18, both surfaces of the wall 18 smoothly expand continuously to their lower edges.