Keynes' relative wage theory has been a strong influence on today's theory which explains the downward rigidity of nominal wage. However, the relative wage theory explains why employees resist underbid of wages in depression, but does not clarify the reason why employers do not cut wages taking advantage of the buyers' market. Also, this theory does not touch the reason why people who lost their jobs do not offer lower wage rate. Theories of involuntary unemployment which have been developed newly in the 1989s strengthen these points and devise their ideas aiming at generalization. These new Keynesians intended to reconstruct the efficiency wage hypothesis proposed by Yellen, J and Shariro = Stigliitz and succeeded in deriving moral hazard based on this hypothesis in order to explain the rigidity of real wages. An important point of the efficiency wage theory lies in that productivity depends on wages. This point was first stressed by the literature on economic development. For employees in developing countries, wages determine their nutrition and are a source of energy for works. One of examples is a concept of the level of the subsistence-wage. But, the new theory advocated by Shapiro = Stiglitz is thought to be applicable even to advanced countries.