A hydraulic driving system includes a flow control valve device, a bleed-off valve device, a discharge pressure sensor, a relief valve, an operating element, and a controller. The controller executes calibration in which: in a state where the bleed-off valve device blocks between a hydraulic pump and a tank, the controller changes a movement command current supplied to the flow control valve device and makes the discharge pressure sensor detect a discharge pressure; the controller detects at least one of an opening start current that is a current when the flow control valve device starts opening and a closing completion current that is a current when closing of the flow control valve device is completed; and based on the detected at least one current, the controller adjusts a correspondence relation between an operation amount of the operating element and the at least one current.