A transmission synchronizer that effectively lowers the peak value of the operation load during synchronization is provided. The transmission synchronizer is equipped with a coupling sleeve, synchro hub, balk ring and clutch gear. A synchronizing support force generating mechanism, during a shift when relative rotation is generated between the synchro hub and the balk ring by a minute synchronizing torque generated between balk ring cone surface and clutch gear cone surface, converts a circumferential force induced by that relative rotation to an axially applied synchronizing support force, with which the balk ring is pressed against the clutch gear. A relative rotation regulating structure is located between the balk ring and the synchro hub, and when in neutral, it regulates the amount of relative rotation between the balk ring and the synchro hub so that the synchronizing support force is not generated.