Since the collapse of the bubble economy at the beginning of the 1990s, Japan has been in secular stagnation. Despite the stagnant economic conditions, the rate of profit has been rising, not falling. The coexistence of the rise in profitability and prolonged economic stagnation is a manifestation of the fundamental contradiction of present-day Japanese capitalism. Marx’s law of the tendency of the rate of profit to fall (LTRPF) provides a consistent explanation regarding the paradoxical situation in Japan characterised not by a falling but a rising rate of profit. Meanwhile, this paper discusses the Monopoly Capitalism school, which has studied capitalist behaviour concerning productive investment and changes in the form of capitalist competition at the monopoly stage of capitalism. While the school’s negation of the LTRPF is unacceptable, their notions may provide useful explanations as to why the rate of profit has risen under secular stagnation in Japan.