To solve the problem that a method for generating image data which processes whole image data by each frame restricts image quality of the image data to be generated by performance of a hardware and image quality is far lower than that of image data generated by spending sufficient time, and a problem that a method for generating image data which switches a plurality of scenarios by a user command can present high-quality image data to the user but restricts the number of scenarios depending on capacity of a storage device, and a degree of freedom the user is allowed is low.

Virtual world data is classified into two kinds as a background part which does not interact with a user and an object part which interacts with the user. As for the background part, high-quality image data is previously generated by spending sufficient time. As for the object part, image data for only a part which does not hide behind the background part is generated in a phase that a way the image data is seen on each frame is determined by the user command.