Provided is a transmission which eliminates torque loss during gear shift and with which the processing of components can be simplified. An axial force is generated in a protrusion by means of a first portion during gear shift from a low gear to a high gear, and when a low-speed transmission gear and a clutch ring separate from each other, a high speed transmission gear and the clutch ring interlock. Since relative movement of the protrusion in a neutral direction is suppressed by means of a first retaining portion during coasting, gear disengagement whereby the transmission gears and the clutch ring separate from each other can be suppressed. Since the first retaining portion can be formed in a first wall when providing a groove portion, an increase in the component processing workload can be suppressed.