A projection system includes a plurality of projectors adapted to project respective images arranged on a projection surface, a control device, and an imaging section, the plurality of projectors is classified into N (N is no smaller than 2) projector groups, the control device makes the projector groups project adjusting images on the projection surface at respective timings different from each other, and then makes the imaging section sequentially image the projection surface on which the adjusting images are projected, at least one of the N projector groups includes two or more projectors, and the two or more projectors project the adjusting images at respective positions not adjacent to each other in the projection surface.