A projected image including at least an image of an overlapping region, on which a first video and a second video are superimposed, is obtained. A correction value for each unit region is determined based on the projected image and an image of a corresponding region in the first video. The corresponding region corresponds to the overlapping region, and the unit region is divided from the overlapping region. Projection-position adjustment based on the correction value is applied to the first video in each unit region.