After World War II, under the guidance of GHQ, the Medical Practitioners Act and the Medical Care Act were enacted, laying the foundations for modern healthcare systems (see Chaps. 3, 4, 5, and 6). However, some citizens could not afford medical care due to poverty. This chapter focuses on the universal healthcare system established in Japan, which was implemented in 1961 [1]. The origin of Japan’s medical insurance system dates to the Health Insurance Act of 1922. The Act was established as a labor policy to address growing concerns about the livelihoods of workers amid rapid workforce expansion and to enhance labor productivity. Subsequently, the former National Health Insurance Act, primarily aimed at assisting farmers, was enacted in 1938. At this time, not all citizens were covered by public health insurance. However, this public health insurance system played a critical role as the basis of the universal health insurance system, which was established after World War II [1].