A hydraulic drive apparatus for hydraulically driving a work machine including a movable element, the hydraulic drive apparatus comprising: a hydraulic pump that discharges hydraulic fluid; a hydraulic actuator coupled to the movable element and operated to actuate the movable element by supply of hydraulic fluid discharged by the hydraulic pump to the hydraulic actuator; a control valve interposed between the hydraulic pump and the hydraulic actuator, the control valve being openable to allow hydraulic fluid to be supplied from the hydraulic pump to the hydraulic actuator; an operation device that makes the control valve open in response to an actuator operation that is applied to the operation device for moving the hydraulic actuator; a pump pressure detector that detects a pump pressure which is a pressure of the hydraulic fluid discharged by the hydraulic pump; an actuator holding pressure detector (63H, 63R) that detects an actuator holding pressure which is a pressure required for holding the hydraulic actuator in a stopped state against a load applied to the hydraulic actuator; an unload valve formed of a pilot-operated selector valve having a pilot port and provided in an unload line which allows hydraulic fluid discharged from the hydraulic pump to bypass the control valve and the hydraulic actuator to return directly to a tank, the unload valve configured to be opened at an opening degree corresponding to a pilot pressure that is input to the pilot port to thereby allow the hydraulic fluid to flow through the unload line at a flow rate corresponding to the opening degree; an unload operation valve formed of a solenoid valve allowing an unload operation command to be input to the solenoid valve, the unload operation valve being operable to change the pilot pressure to be input to the unload valve in response to the unload operation command; and a target pressure calculation part that calculates a target pressure of the pump pressure based on the actuator holding pressure detected by the actuator holding pressure detector (63H, 63R), so as to make the target pressure be a pressure equal to or higher than a minimum pressure required for moving the hydraulic actuator against the load and equal to or lower than a preset restriction pressure; an unload operation command part that generates the unload operation command and inputs the unload operation command to the unload operation valve, characterized in that the unload operation command is a command to make the pump pressure detected by the pump pressure detector follow the target pressure. a hydraulic pump that discharges hydraulic fluid; a hydraulic actuator coupled to the movable element and operated to actuate the movable element by supply of hydraulic fluid discharged by the hydraulic pump to the hydraulic actuator; a control valve interposed between the hydraulic pump and the hydraulic actuator, the control valve being openable to allow hydraulic fluid to be supplied from the hydraulic pump to the hydraulic actuator; an operation device that makes the control valve open in response to an actuator operation that is applied to the operation device for moving the hydraulic actuator; a pump pressure detector that detects a pump pressure which is a pressure of the hydraulic fluid discharged by the hydraulic pump; an actuator holding pressure detector (63H, 63R) that detects an actuator holding pressure which is a pressure required for holding the hydraulic actuator in a stopped state against a load applied to the hydraulic actuator; an unload valve formed of a pilot-operated selector valve having a pilot port and provided in an unload line which allows hydraulic fluid discharged from the hydraulic pump to bypass the control valve and the hydraulic actuator to return directly to a tank, the unload valve configured to be opened at an opening degree corresponding to a pilot pressure that is input to the pilot port to thereby allow the hydraulic fluid to flow through the unload line at a flow rate corresponding to the opening degree; an unload operation valve formed of a solenoid valve allowing an unload operation command to be input to the solenoid valve, the unload operation valve being operable to change the pilot pressure to be input to the unload valve in response to the unload operation command; and a target pressure calculation part that calculates a target pressure of the pump pressure based on the actuator holding pressure detected by the actuator holding pressure detector (63H, 63R), so as to make the target pressure be a pressure equal to or higher than a minimum pressure required for moving the hydraulic actuator against the load and equal to or lower than a preset restriction pressure; an unload operation command part that generates the unload operation command and inputs the unload operation command to the unload operation valve, characterized in that the unload operation command is a command to make the pump pressure detected by the pump pressure detector follow the target pressure.