This paper analyzed the relationship between women's earning ability and marriage formation in Japan. Using data on young Japanese women from the Longitudinal Survey of Adults in the 21st Century (LSA21), it is seen that women's earning ability has a positive effect on marriage formation. Comparison of analysis using different income variables shows that the result is robust. Estimations based on sub-samples of different educational groups indicate that the degree of positive influence of high earnings ability on marriage probability is declining by age for college graduates.