A roller bearing for rotatably supporting a rotating shaft of an internal combustion engine between a main body and a cap of the internal combustion engine. The roller bearing including: a plurality of rollers; a retainer which is cirumferentially splittable and supports the plurality of rollers; and an outer race which is cirumferentially splittable and forms a raceway surface for the plurality of rollers. The retainer is split into a plurality of retaining members. The outer race is split into a plurality of race plates. At least one of the race plates is provided with one of a projection and a cavity to be engaged with one of the main body and the cap to restrict a relative movement between the one of the race plates and the one of the cylinder head and the cap.