PURPOSE: To reduce the sliding resistance of an inward gear and improve the efficiency of a pump by arranging an oil pocket on the sliding surface of a casing or a cover on which the inward gear is slid between the side wall of a pump chamber and a fixed filler.

CONSTITUTION: A pump is provided with a casing 1, a cover 4 fitted on the casing 1, a pump chamber made of a recess 7 formed between both of them 1 and 4, an inward gear 2 slidably provided in the pump chamber, and an outward gear 3 rotatably provided in the pump chamber and driving the inward gear 2 to perform a pump action. In this case, one or more oil pockets 5a-5e are arranged on the sliding surface of the casing 1 or the cover 4 on which the inward gear 2 is slid between the side wall 7a of the recess 7 forming the pump chamber and a fixed filler 8. Oil is guided into the oil pockets 5c-5e from an intake port 11, a pressure oil film floating the inward gear 2 is formed.