To provide an anti-theft device for a construction machine making impossible to release a brake even when the power of a main controller is cut in the case of system down of the construction machine with its engine stopped and the anti-theft device active, in other words, the brake can be released only when a key switch is turned on and a correct code number is entered.

In the construction machine comprising an engine, a main pump driven by the engine, an actuator driven by hydraulic oil supplied from the main pump, the key switch for starting and stopping the engine, a code number input device, a vehicle body controller and an electric circuit having a fuel controller for controlling the operation of an engine speed governor that controls the fuel flow of the engine with electric signals, theft of the construction machine can be prevented by connecting the engine speed governor of the engine to the vehicle body controller via the fuel controller and by stopping the fuel according to a signal of a fuel injection quantity sent from the fuel controller to the engine speed governor when the power of the vehicle body controller is cut.