<p>Marxian economists in Japan have studied the credit system theoretically and developed Marx’s incomplete theory of credit found in Capital Vol.3, Part 5, “The Division of Profit into Interest and Profit of Enterprise”, to explain the logical development of banking credit on the grounds of relationships of commercial credit. The dominant theoretical method has been named “the differentiation and development method” (DDM), in which credit relationships are regarded as developed through the functions of individual industrial capitalists. However, current financial phenomena are undermining these conclusions as financial transactions have expanded irrespective of industrial growth. Meanwhile, recent analyses based on the DDM have proven unable to explain contemporary financial issues, and have been reduced to confusing discussions of market organization.</p><p>This article aims to reconstruct the basic framework of the credit theory of Marxian economics with a focus on its banking theory, the standard being analysis of actual phenomena. Section 1 examines earlier studies and considers their latent methodological fallacies.</p><p>Section 2 dives into the text of Capital Vol.3, Part 5 to discuss two key concepts, “banking capital” and “fictitious capital”. In particular, it examines the text of Chapter 29, “Banking Capital’s Component Parts”, and focuses on the importance of Marx’s attention to the net worth of banks for understanding the concept of capital in the banking industry.</p><p>Section 3 explores the concept of capital and defines it as reserves for non‒performing loans. Banks try to maintain and reinforce their credibility on the basis of this capital, thereby enlarging the scale of their assets with respect to the competition. The growth of such assets leads to an increase in profits even where the interest rate is constant. Financial booms boost the growth of bank assets without maintaining the banks’ credibility, with the result that the banking assets become vulnerable.</p><p>The article ends by proposing that banking be theorized within studies of “the transformation of money into capital” rather than investigated within the DDM framework. This would enable the proper analysis of market organizations in relation to the actions of industrial capitalists.</p>