Extreme programming is the most representative methodology among agile software development methodologies that is agile in business environment which change fast. As software industry is matured, usability of software quality characteristics is emphasized gradually, but effort to obtain usability in extreme programming is insufficient. In this paper, three things lacked in extreme programming are reinforced. First, roles of user interface expert are defined. Second, usability testing method to extreme programming are introduced. Third, development process and products are proposed. The proposed plan is validated by four methods, which analyze supporting software development life cycle, analyze satisfaction of CMM key process areas, analyze satisfaction of CMM practices, and analyze development of green tea shopping mail. Green tea shopping mall is improved 23％ in the estimated running time, 21％ in the learnability. Also, usability is improved 18％ in the heuristic evaluation and 16％ in the questionnaire method.