1. A substrate processing device for processing a substrate, comprising: at least one image sensor for detecting positions of two corners on at least one diagonal line of a substrate when the substrate is moved to a predetermined position; at least one illuminating device that can be disposed so as to illuminate the two corners of the substrate on an opposite side of the substrate at the predetermined position to the at least one image sensor; and a control device designed to determine the position of the substrate, based on the positions of the two corners detected by the at least one image sensor.