Abstract: A one way clutch has a retainer for receiving a sprag intervening between an outer ring and an inner ring. The retainer includes a cylindrical structural body; a stepped flange which radially protrudes from one end of the structural body so that it communicates with a spot facing hole and inner periphery of the outer ring; a sprag receiving groove formed to be cut toward the flange for receiving the sprag; and an elasticity imparting groove formed to an axial direction of the structural body. The flange prevents reduction in the strength of the retainer due to the provision of the sprag receiving groove in the retainer and hence prevents damage of the retainer such as cracking. A remaining portion located at the position corresponding to the elasticity imparting groove imparts elasticity to the retainer.