We propose a simple model describing supply and demand for dental services by patients and by physicians based on assumptions that they maximize their utilities. We consider how the change of the copayment rate affects the supply and demand with the model and also empirically examine the effects after the 1997 reform where the copayment rate of the head of the insured family was raised from 10% to 20%. The doctor visits of the head decreased after the reform, while those of dependents did not. The dental service fee per visit did not change significantly.