A game device for adjusting the progress rate of simulation with the use of a conventional program module for environmental processing is provided. In the game device, a microprocessor (14) selectively performs, in accordance with a game operation provided by a player of a game, either a process for producing environment information which is a basis for a game image of the subsequent predetermined update cycle, and producing a main game image based on the environment information, or a process for repeatedly producing the environment information plural times, and producing a sub game image based on the last produced environment information among the information produced plural times in a shorter time than the main game image.