Abstract: The invention relates to a pump which assures high reliability while maintaining the functionality as a compact, inexpensive motor-mounted internal gear pump. The pump includes an inner rotor with teeth on its outer surface, an outer rotor with teeth on its inner surface to engage with the inner rotor teeth, a pump casing housing both the rotors, and an inner rotor support shaft which pivotally supports the inner rotor. The motor includes a rotator located inside the pump casing, and a stator located outside the pump casing. The pump casing includes two casing members which face both side faces of the outer rotor and the inner rotor and have an outer rotor bearing which pivotally supports both sides of the outer rotor. The inner rotor support shaft has an inner rotor bearing eccentric to the outer rotor to support the inner rotor pivotally in a rotatable manner and connects the two casing members virtually concentrically with the outer rotor bearing.