The internal gear pump according to the present invention includes: an inner rotor; an outer rotor that rotates with predetermined eccentricity to a rotation center of the inner rotor; an outer ring that rotatably holds the outer rotor, and has at least three cam protruded parts formed; a pump housing that has a rotor chamber; pins in the same number as that of the cam protruded parts; and operation means for oscillating the outer ring. Positions of the pins are set so that a diameter center of the holding-inner peripheral part of the outer ring is moved by the operation means along a locus of a circle, the radius of which is the eccentricity to the rotation center of the inner rotor.