1. A method for generating a virtual space object which has a similar shape as a predetermined physical space object, comprising: an input step of inputting a captured image in which said physical space object is captured; an extraction step of extracting a region of said physical space object from said captured image; a generation step of generating an initial virtual space object having a position and orientation corresponding to a position and orientation of said physical space object, said virtual space object having a size to encompass said extracted region; a cutoff step of generating a cut off virtual space object by cutting off part of the initial virtual space object existing at positions not corresponding to said extracted region from a viewpoint from which said captured image is captured; a composition step of generating a composite image of said captured image and a virtual image of the cut off virtual space object, and an output step of outputting said composite image.