In a differential apparatus component (ring gear-integrated with differential case 12), a differential case and a ring gear are formed integrally and seamlessly of cast steel. Cast Steel is preferably composed of 0.3 to 1.0% by mass of silicon (Si), 0.5 to 1.2% by mass of manganese (Mn), 0.1 to 0.5% by mass of vanadium (V), 0.01 to 0.05% by mass of tin (Sn), 0.1 to 1.5% by mass of chromium (Cr), 0.2 to 1.0% by mass of copper (Cu), and the rest composed of iron (Fe) and unavoidable impurities.