To prevent a subject from becoming blur in an arbitrary entire image when a plurality of images are arranged and projected by a multi-projection system.

In the multi-projection system for projecting the entire image onto a screen by arranging a plurality of images in a superposing area such that the images are superposed one on another, an object setting section 15 detects an object from data of the entire image and its position. According to the position of each object detected by the object setting section 15, the superposing-area calculating section 16 calculates the superposing area so that the proportion of the area of each detected object is the maximum in any one of division images.