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 a plurality of bearing portions supporting an 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 interval 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; and the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction. 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 a plurality of bearing portions supporting an 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 interval 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; and the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction. the retainer member is provided with a plurality of bearing portions supporting an 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 interval 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; and the plurality of said bearing portions and the plurality of said holding portions are arranged alternately along the circumferential direction.