In the present invention, a number of times the brightness changes detected at the same position while a substrate conveys are added up in the conveying direction, thereby obtaining a plurality of edge count data, and then, a plurality of positions of long sides of patterns parallel to the conveying direction is identified based on the plurality of edge count data exceeding a predetermined threshold value, middle point positions of a plurality of proximity pairs are calculated, and a middle point position close to the target position preset in the imaging device is selected from the plurality of middle point positions of the proximity pairs, an amount of position displacement between the selected middle point position and the target position of imaging device is calculated, and the photomask in the direction substantially perpendicular to the conveying direction so that the amount of position displacement is a predetermined value.