Internal gear pump

An internal gear pump comprising:

• an inner rotor;
• an outer rotor that rotates with predetermined eccentricity to a rotation center of the inner rotor;
• an outer ring that includes a holding-inner peripheral part rotatably holding the outer rotor and that has at least three cam protruded parts formed along a circumferential direction of an outer periphery surface of the outer ring;
• a pump housing that has a rotor chamber in which the outer ring is freely and oscillatably arranged;
• pins that are in the same number as that of the cam protruded parts and are always brought into contact with the cam protruded parts, and that are installed in the rotor chamber as members separate from the pump housing;
• and operation means for oscillating the outer ring, wherein 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.