A very difficult problem exists regarding windshield shape, and that is to create a balance between aerodynamics and optical distortion. To assist in solving this problem, this study, concerning the characteristics of visual perception for the optical distortion when drivers receive visual information through a windshield, was carried out. In this study, the windshield area was divided into 4 zones from the viewpoints of the level of drivers' fixation frequency and types of objects observed. Distortion was defined as the gap angle ( distortion angle ), which crossed the lines of a grid board with and without a windshield, and distortion angles were measured on a total of 4 windshields. Four drivers indicated areas in each windshield in which they felt the area was distorted. As a result, the thresholds of optical distortion were shown as a function of the horizontal and vertical distortion angles by discriminatory analysis. In addition, it was suggested that the thresholds of optical distortion corresponded with visual contrast sensivity for the spatial-temporal frequency of stimulus luminance about which drivers felt distorted. Finally, we developed a CAD simulation program which enabled estimation of the optical distortion level using windshield shape data, and we used this to investigate effects of the windshield installation angle and driver's eye point on the optical distortion.