In an internal gear pump that includes an inner gear having outer teeth and an outer gear having inner teeth, either the inner or outer teeth have a shape based on a tooth shape that is respectively formed by a generating curve of the outer or inner teeth. The inner teeth are arc-shaped, the outer teeth are curved-shaped, and both end sections of the curved shape are arc-shaped. If a radius of the arc shape of the inner teeth is set as ro, a radius of the arc shape of each of the corner sections is set as ri, a diameter of a pitch circle of the inner teeth is set as dp, and the number of the inner teeth is set as z, the inner gear and the outer gear each has a shape that satisfies a relationship established by following equations: 1.6>ro/(dp/z)>1.0; and ro/(dp/z)>ri/(dp/z)≧0.13. Each of the inner teeth is provided so that an intersecting point between one of arcs that follow the first arc shapes of the adjacent inner teeth and the pitch circle of the inner teeth and in proximity to the other arc is located outside of the other arc.