To improve synchronizing performance by enabling swinging of a thrust piece even when an axial length of a spline part of a hub is short.

In an input gear 16 integral with the spline 16a corresponding to the hub, a support hole 16d in an axial direction which associates with a notch 16b is formed on a flange part 16c, a booster tilt surface 16f is formed on an end of the notch 16b, one end of the thrust piece 32 is inserted into the support hole 16d, and the other end is provided with tilt surfaces 32d and 32e pressing a synchronizing ring 30 and an end surface 32c to which torque is applied from the synchronizing ring 30, the other end side is swung to a rotation direction while having the support hole 16d as a swinging fulcrum when the torque is applied from the synchronizing ring 30, a pressure receiving tilt surface 32f formed on the thrust piece 32 is abutted to the booster tilt surface 16f, and the force in the rotation direction by torque is converted to the thrust in the axial direction, and is transmitted to the synchronizing ring 30.