1. An image rendering device for realizing stereoscopic viewing of composite images generated by compositing background three-dimensional models and foreground three-dimensional models each defined in a three-dimensional modeling space, the image rendering device comprising: a coordinate converter that performs a coordinate conversion on modeling data defining a geometry of a background three-dimensional model and a geometry of a foreground three-dimensional model, so that coordinates describing vertices of the modeling data are converted into three-dimensional coordinates describing corresponding points in the three-dimensional modeling space; a texture mapper that converts background image data into two or more viewpoint textures and maps each viewpoint texture to a background three-dimensional model in the three-dimensional modeling space; a viewport converter that extracts, for each of the two or more viewpoint textures, a viewport image from the background three-dimensional model mapped with the viewpoint texture and from the foreground three-dimensional model; and a manager that manages the foreground three-dimensional model and the background three-dimensional model, wherein the two or more viewpoint textures include an intra-texture object, the manager determines a depth relationship between the foreground three-dimensional model and the intra-texture object, by comparing a parallax of the foreground three-dimensional model occurring in stereoscopic playback with a parallax of the intra-texture object occurring in stereoscopic playback and adjusts a positional relationship between the foreground three-dimensional model and the intra-texture object based on a result of the determination, and the parallax of the foreground three-dimensional model refers to a parallax PS between points SL and SR on a precondition that a point S in the foreground three-dimensional model corresponds to a set of coordinates SL on a left-view viewport and to a set of coordinates SR on a right-view viewport, and is expressed by 
 PS= 2 p *( Sz−D )/ Sz, where Sz denotes a coordinate in a depth direction of a foreground image in a view coordinate system, D denotes a distance between a camera position and a display, and 2p denotes a distance between a left-view camera and a right-view camera.