1. A three-dimensional model data forming apparatus for forming three-dimensional model data of an object sensed by image sensing means, comprising: first detection means for detecting an image sensing position of said image sensing means; second detection means for detecting a lens position of said image sensing means; calculation means for calculating a parameter on the basis of outputs from said first and second detection means; distance distribution extraction means for extracting a distance distribution of the object on the basis of a plurality of images which are sensed by said image sensing means at a plurality of image sensing positions so that the respective images of the object partially overlap each other, and the parameter calculated by said calculation means; three-dimensional model data forming means for forming the three-dimensional model data of the object on the basis of the distance distribution extracted by said distance distribution extraction means, the plurality of images, and the parameter; two-dimensional image generation means for generating a two-dimensional image on the basis of the three-dimensional model data output from said three-dimensional model data forming means; and monitoring means for displaying the two-dimensional image and for designating the displayed two-dimensional image corresponding to a part shape of the object, so that it is possible to visually monitor a forming process for forming three-dimensional model data corresponding to a desired portion of the three-dimensional shape of the object.