A pump rotor is an inner rotor of an internal gear pump, the inner rotor having a tooth profile, wherein a half-tooth portion of the tooth profile is formed of three tooth-profile formation circles that are elliptical or true-circular. Two of the tooth-profile formation circles are a combination of a small tooth-profile formation circle and a large tooth-profile formation circle in which the small tooth-profile formation circle is inscribed and is entirely included. A portion of the small tooth-profile formation circle forms an addendum portion of the half-tooth portion. A portion of the large tooth-profile formation circle in which the small tooth-profile formation circle is inscribed and is entirely included forms an engagement portion of the half-tooth portion. A portion of another tooth-profile formation circle that circumscribes the large tooth-profile formation circle forms a dedendum portion of the half-tooth portion.