In this hydraulic drive system, a hydraulic-oil path forms a closed circuit between a main pump and a hydraulic cylinder. A charge pump replenishes the hydraulic oil in the hydraulic-oil path. A pump control unit performs flow-rate reduction control wherein the intake flow rate of the main pump is reduced so as to be less than or equal to the maximum discharge flow rate of the charge pump when a stroke position is closer to a cylinder-rod stroke end than a prescribed reference position.