A vehicular starter ring gear in the form of an annular member which has external teeth and which is welded at a plurality of positions to a disc member rotated with an engine, such that the vehicular starter ring gear is fitted on an outer circumferential surface of the disc member, so that the vehicular starter ring gear is rotated to start the engine, by a starter motor having a pinion gear engageable with the external teeth, includes: a thermal resistor portion provided in a radial portion between an inner circumferential surface and peak surfaces of the external teeth, and radially outwardly of at least welding portions bridging the vehicular starter ring gear and the disc member, the thermal resistor portion restraining conduction of a heat generated during an operation to form the welding portions, to the external teeth.