This article assesses the Japanese diplomatic contribution through the prism of the Indochinese political situation in the early 1970s. The traditional literature depicts Japan’s non-existent proactivism in postwar foreign politics, based on its alleged unconditional dependence on Washington’s political agenda. However, throughout the 1970s there were occasions in which the country showed how it was independently engaged at a diplomatic level. This has often been overlooked by the literature produced in the field, but it is an irrefutable conclusion from the historical evidence and the analysis of the archival sources. Japan’s diplomatic commitment in solving the problem of peace in Cambodia, its double effort as a diplomatic intermediary between the political actors involved in the Indochinese issue and, at the same time, through the ODA policy, may offer the missing elements for a no longer univocal interpretation of its postwar diplomatic history—which is the aim of this essay.