Even in case that a wafer is so greatly deviated that a peripheral portion of the wafer cannot be detected, position determination of the wafer can be performed without inflicting a damage on the wafer. The wafer peripheral portion, which is a target, is detected based on output images from a plurality of imaging units disposed along a peripheral portion shape of the wafer (step S210), and a wafer position deviation correcting step (step S220) or a rough correcting step (step 230) is performed according to the number of the imaging units capable of detecting the wafer peripheral portion. In case that the wafer peripheral portion cannot be detected by all the imaging units, a wafer position adjusting step (step 240) for moving the wafer is performed in a position adjusting direction acquired by a combination of the output images by each imaging unit.