Web usability in business applications is crucial for enhancing productivity and preventing critical user errors. One of the effective methods to enhance the usability is employment of usability features such as auto-complete and input validation. Then, such employment should be designed so as to conform to actual end-users. However, its evaluation forces developers to expend a lot of effort to design an application, to create its Web prototypes, to observe user operations with the prototypes, and to assess the usability of the employed usability features. In this paper, a framework is proposed for evaluating the usability depending on the employment efficiently even if the developers are non-usability-specialists. Our framework has characteristics as follows so that the developers can easily determine the usability with low creation costs. (1) Support for creating Web prototypes, observing user operations, and assessing the usability are integrated centered on a model-driven approach. (2) The usability can be evaluated relatively and quantitatively by recording user operations and analyzing the resulting logs.