A bearing device comprising: a rolling bearing including a plurality of rolling elements arranged between an inner ring and an outer ring , and a retainer plate configured to retain the rolling bearing to a housing (H) and having a circular hole portion to be fitted to an outer peripheral surface of the outer ring of the rolling bearing , wherein an outer peripheral portion of an axial end portion of the outer ring is provided with a small-diameter step portion to be fitted with the retainer plate , and an outer peripheral surface of the small-diameter step portion is formed with an engagement groove extending in a circumferential direction, wherein an inner peripheral portion of the circular hole portion of the retainer plate is provided with at least three cutout portions , and each of the cutout portions is formed with an engagement protrusion protruding radially inward to be engaged to the engagement groove , wherein an inner diameter-side tip portion of each of the engagement protrusions has a concave shape, wherein at least both circumferential ends of the inner diameter-side tip portion overlap with the engagement groove even at a state where the outer ring and the retainer plate are eccentric or inclined, as seen from an axial direction, wherein the inner diameter-side tip portion of each of the engagement protrusions has a circular arc shape, wherein a radius of curvature of the inner diameter-side tip portion is equal to a radius of curvature of an outer peripheral surface of the small-diameter step portion of the outer ring and substantially the same as the radius of curvature of the cutout portion . a rolling bearing including a plurality of rolling elements arranged between an inner ring and an outer ring , and a retainer plate configured to retain the rolling bearing to a housing (H) and having a circular hole portion to be fitted to an outer peripheral surface of the outer ring of the rolling bearing , wherein an outer peripheral portion of an axial end portion of the outer ring is provided with a small-diameter step portion to be fitted with the retainer plate , and an outer peripheral surface of the small-diameter step portion is formed with an engagement groove extending in a circumferential direction, wherein an inner peripheral portion of the circular hole portion of the retainer plate is provided with at least three cutout portions , and each of the cutout portions is formed with an engagement protrusion protruding radially inward to be engaged to the engagement groove , wherein an inner diameter-side tip portion of each of the engagement protrusions has a concave shape, wherein at least both circumferential ends of the inner diameter-side tip portion overlap with the engagement groove even at a state where the outer ring and the retainer plate are eccentric or inclined, as seen from an axial direction, wherein the inner diameter-side tip portion of each of the engagement protrusions has a circular arc shape, wherein a radius of curvature of the inner diameter-side tip portion is equal to a radius of curvature of an outer peripheral surface of the small-diameter step portion of the outer ring and substantially the same as the radius of curvature of the cutout portion . <EOS>