A radial roller bearing has: an outer ring; an inner ring; and, a cylindrical roller interposed between the outer ring and the inner ring, the outer and inner rings respectively including flange portions formed in the end portions thereof so as to be opposed to the end face of the cylindrical roller, wherein, in the end face of the cylindrical roller, there is formed a circular-ring-shaped contact portion of the roller end having centers of curvature continuously existing on a circle which lies on a plane parallel to the end face of the cylindrical roller and also the center of the circle is on the rotation axis of the cylindrical roller.