A rocking bearing (11, 21, 41, 51, 61) comprising: a fitting structure of a rocking bearing outer ring (12, 22, 32, 42, 52, 62) comprising: a rocking bearing outer ring (12, 22, 32, 42, 52, 62) having an arcuate track member (13, 23, 33, 43, 53, 63) having a track surface (13a, 23a, 43a, 53a, 63a) on an inner diameter surface, and a flange portion (14, 24, 34, 44, 54, 64) projecting radially inward from each widthwise end portion of said track member (13, 23, 33, 43, 53, 63); and a housing for holding the rocking bearing outer ring (12, 22, 32, 42, 52, 62), wherein the following relationship is satisfied 1 < r 1 / r 3 < 1.15 wherein r 1 represents a curvature radius of an outer diameter of said rocking bearing outer ring (12, 22, 32, 42, 52, 62), and r 3 represents a curvature radius of an inner diameter of said housing; a plurality of rollers (15, 25, 45, 55,,65) disposed along said track surface (13a, 23a, 43a, 53a, 63a); and a retainer (16, 26, 46,56, 66) for retaining said plurality of rollers, wherein said flange portion (14, 24, 34, 44, 54, 64) further comprises a projection portion, and wherein the projection portion provided at the tip end of the flange portion (14, 24, 34, 44, 54, 64) holds a projection of the retainer (16, 26, 46,56, 66) from the radially inner side to prevent the retainer (16, 26, 46,56, 66) from dropping out in the radial direction of the rocking bearing outer ring (12, 22, 32, 42, 52, 62), said projection being only provided on the radially outer side of the retainer. a fitting structure of a rocking bearing outer ring (12, 22, 32, 42, 52, 62) comprising: a rocking bearing outer ring (12, 22, 32, 42, 52, 62) having an arcuate track member (13, 23, 33, 43, 53, 63) having a track surface (13a, 23a, 43a, 53a, 63a) on an inner diameter surface, and a flange portion (14, 24, 34, 44, 54, 64) projecting radially inward from each widthwise end portion of said track member (13, 23, 33, 43, 53, 63); and a housing for holding the rocking bearing outer ring (12, 22, 32, 42, 52, 62), wherein the following relationship is satisfied 1 < r 1 / r 3 < 1.15 wherein r 1 represents a curvature radius of an outer diameter of said rocking bearing outer ring (12, 22, 32, 42, 52, 62), and r 3 represents a curvature radius of an inner diameter of said housing; a plurality of rollers (15, 25, 45, 55,,65) disposed along said track surface (13a, 23a, 43a, 53a, 63a); and a retainer (16, 26, 46,56, 66) for retaining said plurality of rollers, wherein said flange portion (14, 24, 34, 44, 54, 64) further comprises a projection portion, and wherein the projection portion provided at the tip end of the flange portion (14, 24, 34, 44, 54, 64) holds a projection of the retainer (16, 26, 46,56, 66) from the radially inner side to prevent the retainer (16, 26, 46,56, 66) from dropping out in the radial direction of the rocking bearing outer ring (12, 22, 32, 42, 52, 62), said projection being only provided on the radially outer side of the retainer. a rocking bearing outer ring (12, 22, 32, 42, 52, 62) having an arcuate track member (13, 23, 33, 43, 53, 63) having a track surface (13a, 23a, 43a, 53a, 63a) on an inner diameter surface, and a flange portion (14, 24, 34, 44, 54, 64) projecting radially inward from each widthwise end portion of said track member (13, 23, 33, 43, 53, 63); and a housing for holding the rocking bearing outer ring (12, 22, 32, 42, 52, 62), wherein the following relationship is satisfied 1 < r 1 / r 3 < 1.15 wherein r 1 represents a curvature radius of an outer diameter of said rocking bearing outer ring (12, 22, 32, 42, 52, 62), and r 3 represents a curvature radius of an inner diameter of said housing; a plurality of rollers (15, 25, 45, 55,,65) disposed along said track surface (13a, 23a, 43a, 53a, 63a); and a retainer (16, 26, 46,56, 66) for retaining said plurality of rollers,