1. An electronic catalogue system for displaying on one screen a image of a commercial product and a image of an article for comparison which is for comparing a size with the commercial product and notifying a size, comprising: reader for reading three-dimensional data of the commercial product and three-dimensional data of the article for comparison; observation image generator for generating an observation image in which the commercial product and the article for comparison are located at predetermined positions based on the read three-dimensional data of the commercial product and three-dimensional data of the article for comparison; and displaying device for displaying the generated observation image.