Between two apexes of a shape model associated with each other, a virtual spring for applying, to the two apexes, a virtual force which is directed in each of coordinate axis directions in a rectangular coordinate system and which is changed in magnitude in accordance with a distance between the two apexes in the coordinate axis direction is set. When positional relationship between the apexes of the shape model is changed from that of a reference state, the game apparatus calculates a difference between the post-change distance between the two apexes and the distance therebetween in the reference state for each of coordinate components. Then, the game apparatus calculates a magnitude of a virtual force generated by each of virtual springs based on the difference; and calculates a virtual force received by each apex for each coordinate component by adding parallel forces among the virtual forces applied to each apex.