A work machine includes a swing hydraulic motor and a swing electric motor for driving an upper swing structure. A capacitor supplies electricity to the swing electric motor and an operating device outputs through one operation, an operating signal for concurrently operating the swing hydraulic motor and the swing electric motor. A main controller switches between a hydraulic-alone drive mode and an electric-alone drive mode, the hydraulic-alone drive mode being a mode to drive only the swing hydraulic motor selected from the swing hydraulic motor and the swing electric motor when the operating device is operated, the electric-alone drive mode being a mode to drive only the swing electric motor selected from the swing hydraulic motor and the swing electric motor when the operating is operated. Therefore, the actuator that malfunctions can easily be specified among the plurality of mounted actuators.