A ratio between an aspect ratio of a digital image signal and an aspect ratio of a display device is converted and a presence image part 2 of digital image data decoded by a digital image signal demodulating part is compressed laterally and is shifted to the center of an image area 1 made of the aspect ratio of the digital image signal and then an absence image part 3 is used as side panels 4 and digital image data made of the aspect ratio of the digital image signal is formed and outputted. Thus, even when the display device converts an image by a lateral uniform expansion method, a display image without lateral expansion can be outputted on a display screen.