The population policies in post-war Japan are argued dividing the period into four. The first period from 1945 to 1959 was the period of so-called over-population when the policies were implemented based on the legislation of Eugenic Protection Law where abortions were legally permitted and favored over contraception to protect the mothers’ health and eugenics, which is based on the idea of counter-selection. The second period from 1960 to 1971 was the period in which the policy of population quality was implemented when the birth rate was thought to be low enough. The third period was the one from 1972 to 1976 when the over-population was argued again and the movement to restrict population growth was promoted while the IUD was officially permitted. The fourth period is from 1977 to the present when the pronatalist policy has been advocated according to the decline of fertility under the replacement level. The development of the implementation of the policy can be articulated into three steps; first: the recognition of the main cause of the fertility decline as the decline of marriage rate, second: the recognition of the cause of the decline of marriage rate as the unfavorable economic situation of younger generation, third: the implementation of policies to attenuate the economic situation of the generation. These steps were gradually taken though the third step has just begun in the 21st century and yet to be virtually effective.