Abstract
There has been a debate about what measurement is most appropriate for measuring inequality because the classical index does not distinguish between what is fair and unfair distribution of income. In this empirical study, the "Responsibility-Sensitive Egalitarian Theory" is applied for the case of Japan. Our paper firstly tracks the historical evolution of inequalities and concludes that the Japanese accept pre-tax income inequality because they believe their socio-economic class is determined by luck. Secondly, illustrating the Unfairness Lorenz Curve by gender shows that females face more unfairness than males: the pre-tax income of middle-income males increases slightly compared to the fair-income group from 2010 to 2013. However,the opposite is true for females in the bottom and middle classes. Considering there already exists a gender wage gap in Japan, it is necessary to take action to reduce inequality.