In this paper, a method of optimization of risk transfer due to earthquake insurance is proposed, which is aimed to be used for a countermeasure of disaster prevention. In this method, a risk is defined by annual expected loss considering a coverage of insurance and an acceptable premium. The coverage of insurance is determined by deductible and limit, and the loss of insured and insurance company can be evaluated in probability mass function with its coverage. Also the acceptable premium can be provided by the function of loss considering subjectivity of decision-makers. The optimal risk transfer is showed by deductible and limit which minimize the risk of insured. The effectiveness of risk transfer and the validity of the proposed method is demonstrated through the numerical example.