A part object which forms a model object is disposed by receiving a disposition direction for the part object and updating slot state data indicating a disposition state of the part object in a part slot provided corresponding to each part object. When another part object has been disposed in the part slot corresponding to the part object for which the disposition direction has been issued, whether or not to update the slot state data of the part slot is determined based on priority information which determines disposition priority of each part object, and the slot state data is updated based on the determination result.