The level of copayment increased in order to stabilize the financial condition of the health insurance on 1986. An important question regarding the policy was whether the increase in the level of copayments reduced the utilization of medical services in the poor selectively. In spite of the importance of the research question, no study has been reported. This study was designed to find out changes in numbers of physician visits, to explain characteristics influencing the difference of utilization before and after the program. Finally the interaction effect between the program and the level of income was examined for the abover question. A total of 10,421 persons from eight institutions was selected as the study sample. Research findings are as follows. 1. The number of physician visits decreased by ten percent as a result of increasing the level of copayment. 2. The decrease was remarkable in some groups such as children, rural area and large family. 3. The most important factor which explained the difference was the number of physician visits before the introduction of the new program. The more numbers of physian visits during the last year were, the more numbers of physian visits decreased after the program. 4. The interaction term between the program and the level of income was statistically significant in the multiple regression model which explained physician visits and its coefficient was negative. It means that an increase in copayment did not reduced the number of physician visits in the poor, selectively. 5. It can be concluded that imposing adequate copayment reduces the use of medical services as well as medical costs without serious damage in access especially for the poor people.