With the improvement in wiping performance of the windshield wiper, the method of evaluating the wiping performance has gained in importance. With the aim of developing a quantitative evaluation method under actual driving conditions which would take into account the driver's visibility, we devised an evaluation system which applies the theory of response function (O.T.F.), which is frequently used in the field of optics in the study of visibility of a solid through an optical medium. We carried out the study by means of model tests and vehicle tests. As a result, we have been able to obtain a wiping performance evaluation system in which quantitative evaluation is possible, taking into account visibility in all kinds of rainfall and driving conditions by using a wind-tunnel device which employs a checked indicator board.