Eye gaze interface has potential as a new HumanComputerInteractionmethod, evidentin the numerouskinds developed so far. However, in order to make sure that such an interface is both useful and convenient in daily life for a wide range of users, we need to undertake more indepth studies of human behavior in order to adapt the design to human factors. In this paper, a prototype system for a menu based interface is described and an experiment designed to analyze users' performance is reported. The results show that 1) the eye gaze interface is faster to operate than the mouse, 2) making selection by means of an eye mark takes longer than just reading menu commands, and 3) most errors are induced by lack of adequate visual feedback from the screen. Based on the results, two methods to reduce selection error and to improve the performance are discussed, and three facts that improve the usability of the eye gaze interface are presented.