The Housing Loan Corporation founded in 1950 was the most powerful supplier of public houses in Japan, which financed the enormous amounts of the Government Housing Loan for Japanese people during the latter half of the 20th century. For instance, approximately sixteen million housing units financed by the Housing Loan Corporation were built from 1966 to 2000, and accounted for about seventy percent of public houses. This research aims to clarify how the Housing Loan Corporation had improved the quality of Japanese houses. To verify the promotion of prefabricated houses by the Government Housing Loan, this paper carries out two approaches: one is to compile the statistic of it and the other is to make a historical review based on the examination of the Housing Loan Corporation's business plans during fifty years. And the followings are clarified. The course of the Housing Loan Corporation's history was to make a variety of loans to the dwelling units for sale. When the Government Housing Loan started in the early 1950s, the customized houses accounted for above ninety percent of the owner occupied dwellings and most of it was loaned to them. But the loans to the dwelling units for sale occupied almost fifty percent of it in the late 1990s. Because the more they were built in Japan, the more the Housing Loan Corporation loaned to them. This suggests that the system of the Government Housing Loan accommodated itself to structural changes of housing market in Japan. The Government Housing Loan to wooden prefabricated houses and steel made a substantial contribution to Japanese houses. The former, based on Agrément on Factory-made Houses since 1966, made an origin of seismic and fire preventive performance with current wooden houses of Japan. The reason is that it grew a structural planning method based on the bearing wall line and a specification of quasi fire resistive construction with wooden materials, which are generally used in designing conventional houses today. In contrast, the latter, started in 1962 as part of noncombustible building policy, seems not to bring anything of technical development. But the Government Housing Loan gave the steel prefabricated houses a quality assurance on new building system, and became the start of spreading tie-up loans in detached houses of Japan. Nowadays steel construction houses occupy approximately twenty percent of Japanese housing market and distinguish it from other countries'. In Europe and America, the purchasers of steel prefabricated houses weren't loaned generally by any financial institutions. This is pointed out to be one of reasons why they didn't take roots there. Therefore, the Government Housing Loan to steel prefabricated houses can be said to become the start of making an identity of Japanese housing market.