A game apparatus, a storage medium, a transmission medium and a program correspond to a normal screen and a wide screen. An image generation unit 150 comprises a wide image data generation unit 152, an image data conversion unit 160 and a rendering unit 154. At first, the wide image data generation unit 152 generates image data viewed from a predetermined viewpoint in an object space, as image data corresponding to the wide screen. Then, the image data conversion unit 160 performs a processing of generating image data corresponding to the normal screen, on the basis of generated wide image data. The rendering unit 154 performs a rendering processing to the generated wide image data or the generated normal image data, and finally generates an image displayed on a display unit 20.