To provide a synchronizing device of a manual transmission capable of preventing the hurting of the gear change feeling caused by the idling of a sleeve in a gear change process by allowing a gear part of a clutch hub to be engaged with a gear part of the sleeve with a larger contact area.

In this synchronizing device providing the synchronous operation by pressing a synchronizer ring by a synchronizer key in a state of moving a sleeve engaged with an outer periphery of the clutch hub in the operating direction of a gear shift lever, and allowing the synchronizer ring to be rubbed while closely abutted on a cone part of the clutch gear, and changing a gear by the engagement of the synchronizer ring and the gear part of the clutch gear by advancing the sleeve into an internal gear part of the sleeve, a number of gear parts of the clutch hub are mounted at equal intervals in the circumferential direction, both side ends of a number of gear parts at this position are extended by a predetermined length to form extension parts, and the synchronizer rings mounted on both sides of the clutch hub are mounted by removing the gear parts corresponding to the extension parts.