An inner rotor having excellent corrosion resistance, which has an outer gear serving as a component of an internal gear pump, and an outer rotor having excellent corrosion resistance, which has an inner gear engaging with the outer gear. The inner rotor and outer rotor of are made of Cu—Ni-based sintered copper alloy that contains 12 to 50% by mass of Ni, 5 to 20% by mass of Sn, 0.5 to 5% by mass of C, and if necessary, further contains 5 to 20% by mass of Zn, 0.1 to 0.9% by mass of P, and a balance being Cu and inevitable impurities.