Various applications have been realized on mobile computers such as smart phones and tablet computers. Because mobile computers have smaller monitors than conventional computers, strategies to develop user interfaces differ from conventional computer applications. For example, contents in a window are reduced or divided into multiple windows on mobile computers. To realize usable applications in this situation, usability evaluations are important. Although various usability evaluation methods for mobile computers have been proposed, few evaluate applications and identify problems automatically. Herein we propose a systematic usability evaluation method. In our method, operation histories by users are recorded and analyzed to identify steps with usability problems. Our method automatically analyzes usability problems, allowing usability evaluations in software development to be implemented easily and economically. As a case study, the operation histories were recorded and analyzed when 20 subjects operated an application on a tablet computer. Our method automatically identified many usability problems, confirming its effectiveness.