A spring clutch is provided for which durability is improved by preventing a clutch spring from breaking due to fatigue. A cylindrical clutch spring made from a wire having a square section is mounted between a pulley and a pulley hub mounted in the pulley. An end of the clutch spring is coupled to the pulley hub. A clutch surface is formed on the inner periphery of the pulley and is formed with a large-diameter recess at a position opposite to the end portion of the clutch spring including the torque transmission end. When the pulley rotates in one direction, the clutch spring expands. At this time, the end portion of the clutch spring including the torque transmission end expands in the large-diameter recess, thus relaxing sharp torque produced in the clutch. This prevents local stress concentration on the clutch spring and breakage of the clutch spring and improves the durability of the clutch.