In an image processing device, an information processing section performs information processing according to an instruction input by a user. An alpha buffer generating block of an image processing section generates an alpha buffer representing, in an image plane, the alpha value of each pixel when designated objects formed by a plurality of objects are collectively regarded as one object. A rendering block reads each piece of model data from an image data storage section, and renders an image also including other objects than the designated objects. A shading processing block approximately calculates degrees of occlusion of ambient light on the image plane, and subjects the rendered image to shading processing on a basis of a result of the calculation.