An over-running clutch has a tube-like clutch outer 23 formed integrally with a boss portion 21 which is helically spline-engaged with an output shaft 1. The clutch outer is slightly diverged toward its open end due to cementation quenching, and has a plurality of grooves formed circumferentially around its inner peripheral surface at an equal pitch. Each of the grooves has a wedge-like shape which gradually decreases around the circumference. A clutch inner 24 accommodated inside the clutch outer is formed such that an axial tilting of its outer peripheral surface is substantially equal to that of the inner peripheral surface of the clutch outer. Rollers are accommodated in each of the wedge-like spaces formed between the grooves and the outer peripheral surface of the clutch inner so as to be circumferentially movable.