1. A game apparatus with which a player plays a game with virtual object(s) in a mixed reality space comprising: viewpoint detection means for detecting the location/posture of a viewpoint of the player; geometric information acquisition means for acquiring geometric information of real object(s); recognition means for recognizing a current, relative relationship between the virtual object(s) and real object(s); a rule memory for storing rules for controlling the action of the virtual object(s); computation means for determining the next action of the virtual object(s) in accordance with the rules stored in said rule memory and in correspondence with the location/posture of the real object(s), and computing thee location/posture of the virtual object(s) after the determined action; and presentation means for generating at least one of image of the virtual object on the basis of the location/posture of the virtual object(s) after the action and the location/posture of the viewpoint position of the player, and for representing the mixed reality space to the player by superimposing the virtual object image(s) on the player's view of the real space.