1. An apparatus which scans an original and a substrate relative to light slit-shaped on the original and on the substrate to expose each of shot regions on the substrate to light via the original, the apparatus comprising: an adjusting device configured to adjust a distribution of a width of the light slit-shaped, the width being a width in a scanning direction as a direction of the scanning, the distribution being a distribution in a perpendicular direction as a direction perpendicular to the scanning direction; and a controller configured to control the adjusting device, wherein the controller is configured to obtain information representing a relationship between a position on the substrate and a target dose, calculate a distribution of the target dose in the perpendicular direction with respect to each of the shot regions based on the relationship represented by the obtained information, and control the adjusting device so as to achieve the calculated distribution of the target dose with respect to each of the shot regions.