PURPOSE: To prevent the rear-end collision of a vehicle even if the fatigue of a driver is severe, by outputting a signal corresponding to the distance between an object to be detected and the vehicle by an infrared detecting output value from the object to be detected positioned in front of the vehicle.

CONSTITUTION: An infrared detector 2 having a calibration curve I wherein the output value of infrared rays issued from an object 8 to be detected at a predetermined temp. is expressed as a value shown corresponding to the distance with the detector 2 mounted therein and outputs a signal corresponding to the distance between a vahicle and the object 8 to be detected by the detected infrared output value. A display alarm apparatus 3 lights a lamp informing that other vehicle appears in front of own vehicle when receives the predetermined output signal from an operator 4 and, when the distance therebetween is brought into a predetermined value, an alarm is emitted. In this situation, a brake mechanism 7 controls the speed of the vehicle and operated in a state controlled by an operation detector 6 and the operator 4.