1. A three-dimensional data processing device for two-dimensionally displaying a three-dimensional space using stereographic data pertaining to a solid body, the device comprising a hardware computer platform which is configured to include: a bounding volume generating unit for generating a bounding volume of the solid body using the stereographic data; a viewpoint setting unit for setting a viewpoint; a view volume setting unit for setting a view volume based on the viewpoint; and a culling processing unit for determining whether or not to draw the solid body within the view volume using the generated bounding volume, wherein the bounding volume generating unit includes a stereographic-data obtaining unit for obtaining the stereographic data, a plane-data obtaining unit for obtaining bottom plane data of the solid body from the stereographic data, an outer-quadrangular-frame obtaining unit for obtaining an outer quadrangular frame that encloses a bottom plane of the solid body defined by the bottom plane data, an inner-quadrangular-frame obtaining unit for obtaining an inner quadrangular frame inscribed within the outer quadrangular frame, wherein the inner-quadrangular-frame obtaining unit is configured to compute the inner quadrangular frame by linking center points on each side of the outer quadrangular frame, a bounding-volume-geometry-data determining unit for determining bounding volume geometry data for generating the bounding volume of the solid body using the inner quadrangular frame as a reference plane, and a bounding-volume output unit for generating the bounding volume of the solid body from the bounding volume geometry data and outputting the generated bounding volume.