First and second division patterns are defined so that main areas A and A′ are similar to each other in shape, having the same horizontal-to-vertical ratio. Even if an image output apparatus is connected to a display unit having both first and second display screens, the image output apparatus generates an identical image for the main area A or A′ regardless of the aspect ratio of the display screen. The main areas A and A′ display important information and the like. Sub areas B and B′ display auxiliary information. The first and second division patterns may be determined so that the sub areas B and B′ are similar to each other in shape like the main areas.