A construction machine, comprising: a work device operable on a drive side and on a regeneration side; an operation device which receives a manipulation and outputs an operation command concerning the work device in accordance with the manipulation; a drive unit for moving the work device, wherein the drive unit includes a hydraulic unit which includes a hydraulic motor as a drive source and drives the work device based on the manipulation on the operation device, and an electric unit which includes an electric motor as a drive source and an energy storage unit functioning as a power source for the electric motor, the electric unit being configured to assist driving of the work device by the hydraulic unit; and a control device (24, 25) which operates the electric unit in such a manner that the electric motor assists the hydraulic unit by electric power from the energy storage unit when the operation device receives a manipulation for actuating the work device on the drive side and which operates the electric unit in such a manner that the electric motor generates regenerative electric power to supply the regenerative electric power to the energy storage unit as charging electric power when the operation device receives a manipulation for actuating the work device on the regeneration side, characterized by a power-discharge command unit which issues a power discharge command to the energy storage unit, wherein the control device (24, 25), in the case where the power-discharge command unit issues the power discharge command, operates the electric motor to lower a voltage between terminals of the energy storage unit when the operation device receives the manipulation for the drive side, and makes only the hydraulic unit to decelerate or stop the work device while not allowing the electric unit to generate the regenerative electric power when the operation device receives the manipulation for the regeneration side. a work device operable on a drive side and on a regeneration side; an operation device which receives a manipulation and outputs an operation command concerning the work device in accordance with the manipulation; a drive unit for moving the work device, wherein the drive unit includes a hydraulic unit which includes a hydraulic motor as a drive source and drives the work device based on the manipulation on the operation device, and an electric unit which includes an electric motor as a drive source and an energy storage unit functioning as a power source for the electric motor, the electric unit being configured to assist driving of the work device by the hydraulic unit; and a control device (24, 25) which operates the electric unit in such a manner that the electric motor assists the hydraulic unit by electric power from the energy storage unit when the operation device receives a manipulation for actuating the work device on the drive side and which operates the electric unit in such a manner that the electric motor generates regenerative electric power to supply the regenerative electric power to the energy storage unit as charging electric power when the operation device receives a manipulation for actuating the work device on the regeneration side, characterized by a power-discharge command unit which issues a power discharge command to the energy storage unit, wherein the control device (24, 25), in the case where the power-discharge command unit issues the power discharge command, operates the electric motor to lower a voltage between terminals of the energy storage unit when the operation device receives the manipulation for the drive side, and makes only the hydraulic unit to decelerate or stop the work device while not allowing the electric unit to generate the regenerative electric power when the operation device receives the manipulation for the regeneration side.