Noise reduction processing for detecting the circumferential edge of a wafer W placed on a rotary stage with a light-transmitting sensor, obtaining detection values provided by the light-transmitting sensor as substrate edge shape data, detecting sudden abnormal data in the substrate edge shape data, eliminating the detected sudden abnormal data and interpolating the substrate edge shape data with estimated data generated based upon surrounding data in place of the abnormal data, notch mark judgment processing for detecting a notch mark candidate in the substrate edge shape data having undergone the noise reduction processing and making a decision as to whether or not the sets of data corresponding to the notch mark candidate area satisfies a predetermined judgment condition, and substrate positioning processing for positioning the substrate based upon a notch mark that satisfies the predetermined judgment conditions are executed.