1. A three-dimensional image generation apparatus comprising: a control unit that transfers a first rendering command which instructs rendering of an object constituting a three-dimensional image; a rendering unit that, upon receiving the first rendering command from the control unit, performs vertex attribute transformation on an object of which rendering is instructed with the first rendering command and renders the object; and a concatenation section that concatenates meshes of a plurality of objects that meet a predefined concatenation condition, the control unit being further provided to perform in advance vertex attribute transformation on the plurality of objects of which meshes are concatenated by the concatenation section, and transfer a second rendering command, the second rendering command instructing rendering of the plurality of objects, on which the vertex attribute transformation has been performed, by regarding the plurality of objects as a single object, the rendering unit being further provided to render, at a time, the plurality of objects that are regarded as the single object, upon receiving the second rendering command from the control unit.