Economic inequality has been a topic of continuing importance in Japan and other advanced economies since the 1990s. Most studies are concerned with economic inequality between individuals or households. Few economists were studying factor shares when T. Piketty’s Capital in the in the Twenty-First Century was published, but, since its publication, much attention seems to have been paid to factor shares and capital–output ratios. This article reviews previous measures of labor's share in Japan and provides alternative estimates of the functional distribution of income for Japan’s non-primary private sector from 1953 until 2014. We will deal with a comparison of alternative measures of labor’s share, focusing on both types of income (wages and salaries, self-employment and mixed incomes, GDP at market prices, NDP at factor costs, and so on) and the economy as a whole (the business and non-business sectors, the corporate sector, and self-employment). In this paper, special emphasis is placed on an estimate of the imputed wages of the self-employed and the other members of their households. Labor income is obtained by adding a component for this mixed income to total employees’ compensation. Estimations of value added, labor income and labor’s share are given in tables in the appendix. Labor's share in the private sector rose moderately in the 1960s, peaking in the late 1970s. Since then, it has fluctuated cyclically and shows neither a general upward nor downward trend, as was already been shown by previous studies.