During a period after starting exposure to a plurality of shot areas subject to exposure on a wafer until completing the exposure, a light via a slit pair arranged on a stage that holds the wafer, of illumination light via a pattern generating device, is received, and information on a positional relation between an illumination light and the stage (and hence a positional relation between the illumination light and the wafer) is detected. With this operation, even if the information on the positional relation between the illumination light and the wafer varies due to some reason, information on the variation can be detected while performing the exposure to the plurality of shot areas. Accordingly, high-precision exposure can be achieved in an exposure operation, by considering this detection results.