A roller gear cam mechanism is equipped with a cam and a rotating member along the outer circumferential direction of which multiple bearings are arranged. The bearings are equipped with a shaft member and an outer ring portion capable of rotating around the shaft member. The outer circumferential surface of the outer ring portion has an arc shape, and in a cross section of the cam that includes the cam axis line, a contact portion of a cam rib making contact with the outer circumferential surface of the outer ring portion has an arc shape. The arc shape of the outer ring portion is formed so as to conform to the arc shape of the cam rib. The radius of curvature of the arc of the outer ring portion and the radius of curvature of the arc of the cam rib are determined in association with each other.