The present invention is about a door 'security system for the providing of the security of the passengers which is standing especially at the middle and back door steps of the vehicles such as buses, midi buses, etc, in accordance with 2001/85 EC policy (Directive 2001/85/EC of the European Parliament and of the Council of 20 November 2001). With the innovation of subject to the present invention, when the door of the vehicle is open, under the condition that there is an object that may be damaged by the movement of the door or the vehicle, by the means of the object sensor with reflector (1, 2) the existence of the concerned object is perceived, and by the means of the relay attached to that sensor, the driver of the vehicle is warned by a visual or audible signal about the existence of the object at the steps.