An apparatus which projects a pattern of an original onto a substrate by a projection optical system within a chamber to expose the substrate, comprises a measurement unit which performs measurement to calculate a deformation amount of the original, and a controller which calculates a predicted deformation amount of the original and corrects a projection magnification of the projection optical system so as to correct the predicted deformation amount, based on information representing a relationship between the deformation amount with reference to a shape of the original at a certain temperature and a time for which the original receives exposure light, a deformation amount of the original before exposure determined based on a measurement value obtained by measuring, by the measurement unit, the deformation amount of the original loaded into the chamber and unused for exposure, and the time for which the original receives the exposure light.