A study on analyze the effect of positive and negative contrast for user performance on the VDT tasks);text typing, text deiting, and searching task) has been performed. The performances were measured in terms of the completion time and the number of errors. The results of each VDT task are followings. In the text typing task and the searching task, the performances measured by the number of errors were better at the condition of negative contrast than at that of positive contrast. In the text deiting task, the performance showed a reverse tendency.