PURPOSE: To prevent the overspeed of an engine by stopping the working of engine brake in the low speed when the speed exceeds the predetermined value during the working of an automatic engine brake means is detected.

CONSTITUTION: During the braking, when a condition which needs the applying of engine brake is occurred, an automatic engine brake means makes an automatic transmission to shift down in the low speed so as to brake effectively. At this stage, an automatic engine brake detecting means detects the actuation of the automatic engine brake means, and an automatic engine brake inhibiting means, corresponding to the detected signal, stops the engine brake when the speed exceeds the predetermined value during the applying of the automatic engine brake. Consequently, under the condition like that the speed is accelerated even if the engine brake is applied at a long down-hill, the shift is backed in the former high speed so as to prevent the overspeed of the engine by travelling in the low speed.