When multiple cameras (CAM1) to (CAM8) for shooting the periphery of a local vehicle are mounted on the vehicle, and when obtained camera images are to be synthesized to display a synthesized image on the screen of a display device (16), the pixel data for the camera images constituting the synthesized image are compensated for, so that differences in the pixel data for adjacent camera images is reduced. For example, the pixel data are corrected so their values equal the average values of the pixel data for the adjacent camera images. Therefore, an easily viewed image, produced by synthesizing the images obtained by the multiple vehicle cameras, can be displayed on the monitor device (16).