The present paper estimates the incidence of the employer portion of social security contributions in Japan. One of the purposes of the paper is to examine whether the employer portion is shifted entirely or partly in many industrialized countries. The paper concludes, based on our estimation method, that there is very little apparent backwards shifting on to employees and, therefore, employers bear nearly all of their portion of social security contributions. Firms in Japan could use their contributions to social security for other purposes to reduce the financial burden on firms. JEL Classification Numbers: H22, J23, J30.