In a one way clutch shipped and transported in a sub-assembly state in which one of inner ring and outer ring is assembled in a later stage. The retainer has pockets radially passing therethrough at predetermined intervals and columns between the adjacent pockets. The circumferential length of each column is so designed as to cause the biasing members, each having a spring force that allows reduction of drug, to exert a biasing force that is so strong that the torque transmission members are prevented by biasing by the biasing members from being dislocated in the sub-assembly state. The circumferential width of an engagement projection of a block bearing is smaller than that of a groove in one of the rings. When a torque greater than a predetermined level is input, the retainer shifts by a distance equal to a gap between the engagement projection and an end of the groove.