Understanding market must be understanding capitalism, because market system is misunderstood as capitalism by many Marxists. However, capitalism can be defined without using the category of market as follows: First, capitalism is a society in which we use machines, and here, quality and quantity of products are determined not by worker's skill but by quality and quantity of machines, and workers become unskilled and just affixes. And the most important change from the feudalist system was their weak bargaining power against capitalists, because now capitalists can gather unskilled workers easily from labor market. Now, anyone in labor market can substitute workers in their factories. Therefore, under this condition, workers' wages become lower and profits become higher, and most part of profits are used reinvestment and sizes of machines become larger. Here, because we assumed that sizes of machines determine sizes of products after the industrial revolution, this re-investment means economic development. That is, the capitalist way of economic development! In this explaining, we can understand why we need capitalism after the industrial revolution where machines became the most important factors of production, and in this sense, this understanding is very materialistic and historical. This is the reason why our understanding has to be regarded as a part of Marxist theory. Therefore, our problem is whether market is needed for this capitalism or not. Of course, I also think that market sometimes enforces workers to work hard to avoid their companies' bankruptcy. It is true and the reason why we are against markets now. However, Stalin and Mao also realized a rapid capital accumulation without using market system, and it also can be understood as a kind of capitalist development based on the above framework. In this sense, market is not needed for the definition of capitalism. In addition, 'private ownership' is not needed for this by the same reason. One more topic related to this problem is the relationship between managers and workers in the post-capitalist era, if we don't need nationalization of the private enterprises, and in this sense, we put importance on the present trend of disclosure of inner information of enterprises. Of course, still now this disclosure is not sufficient to be controlled by the public, but if it will become sufficient and effective, we can understand it is like a public ownership, because we can control them. Before, prof. Okishio said that the nature of ownership is who has the right of decision-making, and in this sense, such control by the public can be understood as a kind of public ownership. I know that this new Marxism is not its original one and still now is not accepted by the orthodoxy. However, we cannot deny that this is a kind of historical materialism, and in this sense, it belong to the tradition of Marxism. In this paper, we also explained that our way to avoid 'over-accumulation' and terminate class division is not through governmental intervention but through stock market. However, in the nature, it is same as Marx's way, and completely different from the ways of social democrat and trade unionism because they don't terminate class division itself.