A one-way clutch having: an inner race; an outer race arranged on a center axis of said inner race coaxially therewith, a plurality of cam members interposed between said inner race and said outer race to serve torque transmission between said inner race and said outer race; a retainer member for holding the plurality of said cam members; and a spring member biassing the plurality of said cam members to no torque transmitting positions, being characterized in that: the retainer member is provided with an annular plate arranged on said center axis, said plate member being provided on one axial side surface thereof with a plurality of bearing portions supporting the inner circumferential surface of said outer race, and the same number of holding portions as the number of said bearing portions, the holding portions each holding two or more predetermined number of said cam members with predetermined intervals along the circumferential direction; the plurality of said bearing portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly, the plurality of said holding portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly; the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction; and the annular plate is formed with a plurality of cut-away portions (43, 45) extended radially. an inner race; an outer race arranged on a center axis of said inner race coaxially therewith, a plurality of cam members interposed between said inner race and said outer race to serve torque transmission between said inner race and said outer race; a retainer member for holding the plurality of said cam members; and a spring member biassing the plurality of said cam members to no torque transmitting positions, being characterized in that: the retainer member is provided with an annular plate arranged on said center axis, said plate member being provided on one axial side surface thereof with a plurality of bearing portions supporting the inner circumferential surface of said outer race, and the same number of holding portions as the number of said bearing portions, the holding portions each holding two or more predetermined number of said cam members with predetermined intervals along the circumferential direction; the plurality of said bearing portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly, the plurality of said holding portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly; the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction; and the annular plate is formed with a plurality of cut-away portions (43, 45) extended radially. the retainer member is provided with an annular plate arranged on said center axis, said plate member being provided on one axial side surface thereof with a plurality of bearing portions supporting the inner circumferential surface of said outer race, and the same number of holding portions as the number of said bearing portions, the holding portions each holding two or more predetermined number of said cam members with predetermined intervals along the circumferential direction; the plurality of said bearing portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly, the plurality of said holding portions is respectively arranged, with respect to said center axis, at diagonal positions along the circumferential direction equiangularly; the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction; and the annular plate is formed with a plurality of cut-away portions (43, 45) extended radially.