A pump system includes a housing, an input shaft, a pump shaft; a hydraulic pump body, a PTO shaft, a power transmission gear train, and a PTO clutch mechanism. The housing has a narrow gear accommodating space surrounding a region including a mesh point between the first and second transmission gears of the power transmission gear train, a PTO clutch accommodating space which surrounds the PTO clutch mechanism and which is fluidly communicated with the gear accommodating space, and a pair of first and second suction/discharge ports which communicate the internal space of the housing with an outside of the housing. The first suction/discharge port is arranged within the gear accommodating space so as to be positioned in an opposite side to the PTO clutch accommodating space with the mesh point between the first and second transmission gears interposed therebetween.