PURPOSE: To accurately find a range by projecting two kinds of pattern images which are in negative-positive relation on a subject, finding the mean value of image intervals found by the pattern images, and finding the distance to the subject by using the mean value as a correct image interval.

CONSTITUTION: The two kinds of pattern images A and B which are projected on the subject are in the negative-positive relation, so the edge parts which are inverted in brightness are at the same positions in the respective pattern images. Then the gradients corresponding to the edge parts in photoelectric conversion signals corresponding to the images formed on the image pickup element are inverted corresponding to the respective patterns. An error d corresponding to an image interval (d) is equal in absolute value and opposite in sign between one pattern and the other pattern and the means value of the image intervals obtained from the respective patterns is a correct image interval after the error ±d is removed. Consequently, the image interval on which range finding arithmetic is based on accurately be measured and the accurate range finding operation becomes possible.