PURPOSE: To display an image without deterioration by performing the coordinate conversion of a device coordinate system so that the longitudinal/lateral ratio of an area corresponding to pixels becomes the reciprocal of the longitudinal/lateral area of the pixels, and performing a rendering process.

CONSTITUTION: The device coordinate system corresponding to a sight direction is set. The coordinates of the device coordinate system are converted so that the longitudinal/lateral ratio of the area corresponding to the respective pixels 21a of a display screen 21 on the device coordinate system becomes the reciprocal of the longitudinal/lateral ratio of the pixels 21a. A conversion program is previously generated and stored in a storage device 16. Then a controller 12 generates image data on the device coordinate system, defined by the X, Y, and Z axes after the conversion, by rendering on the basis of model data and a display object is displayed as a set of pixels on a display screen by using the image data.