A hydraulic driving apparatus for respectively driving a first driving subject and a second driving subject included in a work machine by means of a hydraulic pressure, comprising: a first pump motor that can be switched between a first pump operation state of being driven by a prime mover, thereby sucking hydraulic oil for, in use, driving the first driving subject from a tank, and discharging the hydraulic oil and a first motor operation state of receiving a supply of the hydraulic oil, thereby generating power; a second pump motor that is, in use, coupled to the first driving subject, and can be switched between a second motor operation state of receiving a supply of the hydraulic oil discharged from the first pump motor in the first pump operation state, thereby moving the first driving subject and a second pump operation state of receiving a supply of energy held by the first driving subject, thereby operating so as to suck the hydraulic oil from the tank, and discharge the hydraulic oil; a first pump motor line that connects the first pump motor and the second pump motor with each other so that the hydraulic oil can be supplied from the first pump motor to the second pump motor; a first accumulator that is connected to the first pump motor line, and receives the hydraulic oil discharged from the second pump motor in the second pump operation state, thereby accumulating a pressure; characterised by a pressure holding valve that is interposed between the first accumulator and the first pump motor, and preventing a pressure release from the first accumulator to the first pump motor so as to hold the pressure in the first accumulator; a regeneration subject hydraulic actuator that is, in use, coupled to the second driving subject, and receives a supply of the hydraulic oil, thereby moving the second driving subject; a hydraulic pump that sucks the hydraulic oil to be supplied to the regeneration subject hydraulic actuator from the tank, and discharges the hydraulic oil; a second accumulator that, in use, receives the hydraulic oil pressurized by means of energy held by the second driving subject, and discharged from the regeneration subject hydraulic actuator, thereby accumulating a pressure; a second pump motor line that connects the second accumulator to the first pump motor so that the pressure of the hydraulic oil accumulated in the second accumulator is released to the first pump motor in the first motor operation state, thereby enabling the drive of the first pump motor; and a pressure release changeover valve that can be switched between an open state of opening the second pump motor line, thereby enabling the pressure release from the second accumulator to the first pump motor and a closed state of blocking the second pump motor line, thereby blocking the pressure release. a first pump motor that can be switched between a first pump operation state of being driven by a prime mover, thereby sucking hydraulic oil for, in use, driving the first driving subject from a tank, and discharging the hydraulic oil and a first motor operation state of receiving a supply of the hydraulic oil, thereby generating power; a second pump motor that is, in use, coupled to the first driving subject, and can be switched between a second motor operation state of receiving a supply of the hydraulic oil discharged from the first pump motor in the first pump operation state, thereby moving the first driving subject and a second pump operation state of receiving a supply of energy held by the first driving subject, thereby operating so as to suck the hydraulic oil from the tank, and discharge the hydraulic oil; a first pump motor line that connects the first pump motor and the second pump motor with each other so that the hydraulic oil can be supplied from the first pump motor to the second pump motor; a first accumulator that is connected to the first pump motor line, and receives the hydraulic oil discharged from the second pump motor in the second pump operation state, thereby accumulating a pressure; characterised by a pressure holding valve that is interposed between the first accumulator and the first pump motor, and preventing a pressure release from the first accumulator to the first pump motor so as to hold the pressure in the first accumulator; a regeneration subject hydraulic actuator that is, in use, coupled to the second driving subject, and receives a supply of the hydraulic oil, thereby moving the second driving subject; a hydraulic pump that sucks the hydraulic oil to be supplied to the regeneration subject hydraulic actuator from the tank, and discharges the hydraulic oil; a second accumulator that, in use, receives the hydraulic oil pressurized by means of energy held by the second driving subject, and discharged from the regeneration subject hydraulic actuator, thereby accumulating a pressure; a second pump motor line that connects the second accumulator to the first pump motor so that the pressure of the hydraulic oil accumulated in the second accumulator is released to the first pump motor in the first motor operation state, thereby enabling the drive of the first pump motor; and a pressure release changeover valve that can be switched between an open state of opening the second pump motor line, thereby enabling the pressure release from the second accumulator to the first pump motor and a closed state of blocking the second pump motor line, thereby blocking the pressure release.