A large hydraulic excavator permits an easy change from a machine mode corresponding to a backhoe excavator to a machine mode corresponding to a loader excavator, and vice versa. A hydraulic circuit is provided with hydraulic pumps and directional control valves, solenoid valves for controlling the hydraulic pumps and the directional control valves, and a controller for controlling the solenoid valves in accordance with operation of control lever devices and control pedal devices. The controller performs its control in a backhoe mode or loader mode selectively instructed by a mode instruction unit. Control of the solenoid valves in the backhoe mode makes the hydraulic circuit function as a backhoe hydraulic drive circuit, while control in the loader mode makes the hydraulic circuit function as a loader hydraulic drive circuit.