1. As object extracting method of extracting a position of an object in a to-be-inspected region through an image processing, comprising the steps of: obtaining a plurality of density values of brightness from an image of the to-be-inspected region picked up by an image pick-up device; converting the density value which is larger than a present first threshold value into a specified upper value and converting the density value which is smaller than a preset second threshold value into a specified lower value, the preset first threshold being higher than the preset second threshold, one of the threshold values being set for the object and the other of the threshold values being set for a region other than the object so that the density value of the object is clearly different from that of the region other than the object; integrating the density values at an X coordinate on a Y axis or a Y coordinate on an X axis; projecting the integrated density values on the selected axis; and extracting the position of the object present in the to-be-inspected region based on differences in adjacent integrated density values.