1. An exposure method in which overlay exposure to a photosensitive object is performed by overlaying layers, the method including: a selection process in which a reference layer that serves as a reference to obtain information on overlay exposure of a next layer is selected for each of axes of a two-dimensional orthogonal coordinate system that serves as a reference on overlay, from among at least two layers that have been already exposed, wherein the information on overlay exposure includes a distortion component of a projected image at the point in time when exposure of the reference layer was performed, in a projection exposure apparatus that was used for the exposure of the reference layer.