1. An apparatus which scans an original and a substrate relative to slit-shaped light 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 slit-shaped light, 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, the adjusting device including a pair of light-shielding members, and an actuator configured to tilt at least one of the pair of light-shielding members relative to the perpendicular direction to adjust the distribution of the width; 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 by approximating the relationship represented by the obtained information with a function that is linear with respect to a variable representing a position in the perpendicular direction, and control the adjusting device so as to achieve the calculated distribution of the target dose, approximated with the linear function, with respect to each of the shot regions.