This paper discusses VDT syndrome from the point of view of viewing distance between the surface of a computer screen and the user's eyes. This paper conducts a pilot experiment to show an impact of viewing distance to task performance. In the experiment, two different viewing distances of 50 cm and 350 cm with the same viewing angle of 30 degrees, resulting in 24 inch computer screen at 50 cm away from the user and 200 inch projection screen at 350 cm away from the user, are taken into consideration. Subjects were asked to perform two tasks: a simple mouse manipulation task of Tapping test and a simple calculation task of Kraepelin test. The result shows that viewing distance tends to affect accuracy of mouse manipulation and calculation tasks.