An object region detection unit (130) decides the region of a physical object of interest in a physical space image. An image manipulation unit (140) performs shading processing of an inclusion region including the decided region. A rendering unit (155) arranges a virtual object in virtual space at the position and orientation of the physical object of interest and generates a virtual space image based on the position and orientation of the user's viewpoint. A composition unit (160) generates a composite image by superimposing the virtual space image on the physical space image that has undergone the shading processing and outputs the generated composite image to an HMD (190).