1. A multiprojection display system in which a plurality of projectors project images onto a screen, and a plurality of projected images are connected on the screen to form one screen, comprising: a plurality of cameras, installed in positions to be able to capture images of image-capturing regions including, marks whose visible light reflection ratio is higher than the projection region of said screen and/or support members whose ratio to reflect visible light is different from the projection region and configured to support said projection region; an image processing circuit that detects the prescribed positions in which vertexes of the projected images must be set on said screen and positions of the vertexes of said projected images based on captured image data acquired by capturing the images of said image-capturing regions by said cameras, and outputs data indicating the detected prescribed positions and image edge data indicating the positions of the vertexes of said projected images; and a control unit that adjusts, when the positions of the vertexes of said projected images shift from the prescribed positions corresponding to the vertexes, positions and sizes of said projected images based on the data indicating said prescribed positions and said image edge data so that the positions of the vertexes of said projected images match said prescribed positions.