PURPOSE: To quickly and easily adjust deviation from a lane without using a specific device even in an environment such as a vehicle production line by generating an alarm based upon positional relation between the horizontal position data of a detected lane and the positional data of the right and left side ends of a vehicle.

CONSTITUTION: When a marker arranged on a prescribed outside point corresponding to a pan direction allowable error on the right and left side ends of a vehicle is photographed by a line camera 1 arranged on a prescribed front center of the vehicle, a picture processor 3 previously stores the horizontal position data of a binary picture of the marker in a memory 6 as the positional data of the right and left side ends of the vehicle. When an alarm is generated based upon the positional relation between the detected horizontal positional data of the vehicle and the positional data of the right and left side ends of the vehicle, the fixing error of the camera 1 is corrected/absorbed. Thereby the fixing error can be quickly and easily adjusted without executing complicated and fine adjustment for the fixing angle of the camera 1.