To simplify piping, to save a space for the same, to facilitate maintenance and inspection, to simplify a pump structure and to reduce costs in a twin integrated gear pump.

Two pump bodies wherein main driving shaft gears 3a, 3b and driven shaft gears are meshed and rotated inside inner casings 4a, 4b having inlets 13a, 13b and outlets 15a, 15b on upper and lower parts through seal flange parts 12a, 12b, are assembled in an outer casing 8 of an integral structure having suction ports 20a, 20b and delivery ports 21a, 21b, and having two internal spaces 18a, 18b difined into low pressure chambers 18a (L), 18b (L) vertically partitioned by partitioning plate parts 22a, 22b and communicated with the suction ports 20a, 20b, and high-pressure chambers 18a (H), 18b (H) communicated with the delivery ports 21a, 21b to form twin integrated gear pump.