1. An image retrieval method of a computer for retrieving similar objects, comprising: reading from a first database a plurality of images of an image group mapped to a multidimensional object as a retrieval target, and extracting an image feature quantity of the read plurality of images, the first database storing the plurality of images depicting the multidimensional object as the retrieval target from a plurality of orthoprojection viewpoints of the multidimensional object in different directions; reading from a second database a plurality of images of an image group mapped to a multidimensional object as a search key, and extracting an image feature quantity of the read plurality of images, the second database storing the plurality of images depicting the multi-dimensional object as the search key from a plurality of orthoprojection viewpoints in different directions; determining a similarity between the image group mapped to the multidimensional object as the search key and the image group mapped to the multidimensional object as the retrieval target, based on the image feature quantity of the plurality of images of the image group mapped to the multidimensional object as the retrieval target and the image feature quantity of the plurality of images of the image group mapped to the multidimensional object as the search key; and displaying, on an output device, as retrieval results the plurality of images of the image group mapped to the multidimensional object as the retrieval target in an order of similarity of the multidimensional object as the retrieval target based on the determined similarity, wherein the retrieval results are presented by displaying the multidimensional object as the search key in a cubic diagram using the plurality of images of the multidimensional object as the search key, and by displaying the multidimensional object as the retrieval target in another cubic diagram using the plurality of images of the multidimensional object as the retrieval target.