To provide an object position detecting method rightly finding the position and the lateral width of an object, an existing range of the object, and the locus of the central position of the object, even if a part of the object goes off the detection angle.

The distance to the object existing in the detection angle, the direction, and the lateral width of the object are measured, a moving vector of the lateral position of the object for the distance and the direction of the object under the measurement is measured, the lateral width of the object under measurement is stored, and when it is determined that a part of the object under measurement goes off the detection angle, the position of the par being off the detection angle is interpolated based on the stored lateral width of the object and the moving vector of the lateral position of the object measured in the detection angle.