The variable displacement gear pump for a loading system in an industrial vehicle has main and sub gear pump portions, suction, discharge and bypass passages, and check and opening valves. The main gear pump portion has main drive and driven gears, and has suction and discharge side spaces. The sub gear pump portion has sub drive and driven gears, and has suction and discharge side spaces. The bypass passage returns hydraulic fluid in the discharge-side space of the sub gear pump portion to the suction passage. The check valve prevents hydraulic fluid in the discharge-side space of the main gear pump portion from flowing to that of the sub gear pump portion. The opening valve is used for opening and closing the bypass passage, and closes the bypass passage due to a pressure in a discharge conduit of the loading system increased by the load applied to the loading system.