A shovel with a plurality of hydraulic pumps (14L, 14R), the shovel comprising: a hydraulic swing motor; a relief valve configured to release hydraulic oil when a pressure of hydraulic oil that is released from the hydraulic swing motor becomes higher than a relief pressure; a hydraulic motor configured to generate an engine-assist torque in response to hydraulic oil flowing out of a suction port side of the hydraulic swing motor during swing acceleration, or in response to hydraulic oil flowing out of a discharge port side of the hydraulic swing motor during swing deceleration; an accumulator configured to accumulate the flowing out hydraulic oil; characterized by an open/close valve, whose open area is adjustable, configured to switch open/close of transfer from one of the suction port and the discharge port to both the hydraulic motor and the accumulator; and a control device configured to control the open/close valve, wherein the control device adjusts an open area of the open/close valve during the swing deceleration to cause a pressure of the flowing out hydraulic oil to be a predetermined target pressure, and causes the flowing out hydraulic oil to flow into each of the hydraulic motor and the accumulator at the same pressure, and the control device controls the open area of the open/close valve to cause a swing flowing-in pressure detected by a swing pressure sensor to become a swing acceleration target pressure by using an accumulator pressure and the swing flowing-in pressure during the swing acceleration and adjusts a displacement volume of the hydraulic motor to cause the engine-assist torque to become an assist torque target value. a hydraulic swing motor; a relief valve configured to release hydraulic oil when a pressure of hydraulic oil that is released from the hydraulic swing motor becomes higher than a relief pressure; a hydraulic motor configured to generate an engine-assist torque in response to hydraulic oil flowing out of a suction port side of the hydraulic swing motor during swing acceleration, or in response to hydraulic oil flowing out of a discharge port side of the hydraulic swing motor during swing deceleration; an accumulator configured to accumulate the flowing out hydraulic oil; characterized by an open/close valve, whose open area is adjustable, configured to switch open/close of transfer from one of the suction port and the discharge port to both the hydraulic motor and the accumulator; and a control device configured to control the open/close valve, wherein the control device adjusts an open area of the open/close valve during the swing deceleration to cause a pressure of the flowing out hydraulic oil to be a predetermined target pressure, and causes the flowing out hydraulic oil to flow into each of the hydraulic motor and the accumulator at the same pressure, and the control device controls the open area of the open/close valve to cause a swing flowing-in pressure detected by a swing pressure sensor to become a swing acceleration target pressure by using an accumulator pressure and the swing flowing-in pressure during the swing acceleration and adjusts a displacement volume of the hydraulic motor to cause the engine-assist torque to become an assist torque target value.