An exposure method wherein a focus measuring pattern is successively projected onto focus-measuring points on a wafer (W) while changing the position of the wafer (W) along the optical axis (AX). Then, from the results of projection exposure of the focus measuring pattern, the position of the best image formation plane of a projection optical system (PL) at each measurement point is determined. By using the positions of the best image formation planes, the target focus level of a multi-point autofocus sensor is calibrated. Even when the environment of the projection optical system changes, a high detection precision of the multi-point autofocus sensors can be maintained for each sensor. This exposure method is particularly effective in aligners using a projection optical system with a large numerical aperture.