Evaluating the benefits of disaster mitigation action quantitatively and sharing these results with the society are extremely useful in promoting mitigation action. Many studies, however, have focused on the investigation of the damage but not on the mitigation effects of preparedness. Hence, this study analyzed the mitigation effect of the Business Continuity Plan (BCP) on financial damage to non-manufacturing industries in the Great East Japan Earthquake. Our analysis showed the following: 1) In many companies, there is no difference in the direct damage to the company group with BCP and to the group without BCP. 2) The sales of the damaged group without BCP decreased about 5% compared to those of the damaged group with BCP for more than two years. In other words, the effect of mitigating financial damage by BCP is more than 10% of annual sales on the average. 3) The relationship between BCP and sales was analyzed under limited variables, and the coefficient of BCP showed positive effect on sales with significance at a 5% level. Although our result is only an indication, it could be said that this finding, which shows cost-benefit information on BCP, is useful to promote BCP.