In a rendering device Urnd1, a processor 1 receives a front-left image Sfl and a front-right image Sfr at regular intervals, and therefrom, cuts out a partial front-left image and a partial front-right image for overlay onto a mask image. The processor 1 then overlays, with a predetermined timing, any one of vehicle model images varying in size onto the mask image. Here, the vehicle model image is overlaid in such manner as to create a moving picture as if the vehicle model image is moving forward. With such vehicle model image, a driver of a vehicle can instantaneously recognize that a drive assistant device is now showing the front side of the vehicle.