As many industrial workers have been involved with computer terminal tasks, for example, monitor ing, inspection, or computer da4a entry etc., concerns for difficulty evaluation of computer terminal tasks are Increased. This study provides that eyeblink can be used as a means of difficulty evaluation of a computer terminal lask. Four subjects without color blindness are asked to perform the monitoring task of the binary choice type under five levels of task difficulty. In each task, eyeblink rates and eyeblink interval times were measured from the subjects. The results show that the eyeblink rate does decrease with an Increase in task difficulty. In addition, it was found that both eyeblink interval time and eyeblink Interval time variation increased with an increase in task difficulty. It was concluded that the change of eyeblink rate, eyeblink interval time and eyeblink interval time and eyeblink interval time variation could be regarded as a generalized response to the imposition of task difficulty.