1. An object manipulation method of manipulating an object displayed on a display apparatus for deformation, the object manipulation method comprising: setting, by a control apparatus configured to control the display apparatus, a polyhedron with a given point in the object being a center; dividing, by the control apparatus, a space inside the polyhedron by a vector going from the center of the polyhedron to an apex of the polyhedron; discriminating, by the control apparatus, in which of the divided spaces an apex of the object is included; storing, by the control apparatus, a decomposition coefficient of the apex of the object by three vectors making up the space including the apex of the object; and deforming, by the control apparatus, the object in accordance with the deformation manipulation acted on the polyhedron and displaying the deformed object.