1. An image processing apparatus for simulating an eyesight of vision disorder which generates a composite image of a real image and a virtual image, comprising: a storage unit adapted to store a first parameter and a second parameter to generate an image corresponding to an eyesight characteristic of vision disorder; an acquisition unit adapted to acquire a real image; a conversion unit adapted to convert the real image acquired by the acquisition unit into a real image simulating the eyesight of the vision disorder on the basis of the first parameter; a generation means unit adapted to generate a virtual image simulating the eyesight of the vision disorder on the basis of the second parameter, the virtual image corresponding three dimensional model data; a composition unit adapted to generate a composite image of the real image converted by the conversion unit and the virtual image generated by the generation unit; and a display unit adapted to display the composite image by the composition unit.