To provide an internal gear pump having reduced variation of a clearance between an outer rotor and a case.

In this internal gear pump comprising the outer rotor 1 having an internal gear part 1a on its inner periphery, an inner rotor 2 having an external gear part 2a engaged with the internal gear 1a of the outer rotor 1, and the case 3 for accommodating the outer rotor 1 and the inner rotor 2 rotatably in a state of being eccentric to each other, the outer rotor 1 comprises a rotor body 5 having the internal gear part 1a, and a gutter ring 6 fitted to an outer periphery of the rotor body 5, and the gutter ring 6 is made of a material having a linear expansion coefficient smaller than that of the rotor body 5.