A transformation-based Web site can keep the content of a Web site consistent by furnishing a single database and a set of transformation programs, each of which generates a Web page. However, when someone notices an error or stale content on a Web page in this style of Web site construction, the Web site maintainer must access a possibly huge database to update the corresponding content. This paper proposes a new approach to Web site construction based on bidirectional transformation, together with a practical updating system, Vu-X. Because of the bidirectionality of the transformations, users can directly modify a generated Web page rather than accessing the database and the modification is automatically reflected in the database. The Vu-X system is also implemented as a Web server so that users can edit it in WYSIWYG style on their Web browsers. Since the Vu-X system employs a bidirectional transformation language Bi-X to describe bidirectional transformations, we can obtain both transformations only by specifying a transformation in one direction.