In an apparatus for evaluating reliability of a nuclear power plant operator, an expected task finishing time for each task of the operator is calculated based on input data for reliability evaluation of the operator to determine a task completion time for each task of the operator based on the calculated expected task finishing time and the input data. An initial time for the tasks is determined based on the input data and the task completion time for a current task. A total execution time of the operator is calculated based on the determined task completion time and initial time. An available time allowed for the operator to complete the tasks is calculated based on a predetermined allowed time and the determined initial time. A task failure probability is obtained from the difference between the calculated total execution time and the calculated available time based on probability distribution information.