An image generation device generates a mosaic image which is suitable for users to see even if sufficient images are not acquired to complete the mosaic image. The image generation device specifies, in units of divided areas, an image area in which an image is drawn in each layer of a plurality of layers divided into the plurality of divided areas, allocates the acquired image to the divided areas in the image area of one of the layers, based on color information of the acquired image and color information of each of the divided areas in the specified image area, and generates a mosaic image by superimposing, between layers, the image allocated in the image area of two or more layers of the plurality of layers in which an image is allocated to at least one of all of the divided areas in the image area of each of the layers and the divided areas of another layer having a display position which overlaps the divided areas.