Hydraulic drive device

A hydraulic drive device that drives a hydraulic cylinder by supplying and draining a working fluid to and from each of a head-end port and a rod-end port of the hydraulic cylinder, the hydraulic drive device comprising:

• a hydraulic pump motor that discharges the working fluid and is rotatably driven by the working fluid;
• an electric motor connected to the hydraulic pump motor;
• a directional control valve that switches a direction of the working fluid flowing between the hydraulic pump motor and the head-end port;
• a regeneration valve that opens and closes a regeneration passage connecting the head-end port and the rod-end port;
• a pressure sensor that measures inflow pressure at the hydraulic pump motor;
• and
• a control device that controls an operation of each of the directional control valve and the regeneration valve, wherein:
• when causing the regeneration valve to open the regeneration passage and causing the directional control valve to connect the head-end port and the hydraulic pump motor, the control device controls an opening degree of the regeneration valve according to the inflow pressure of the working fluid that is measured by the pressure sensor.