The following is from Wikipedia which is related with Treaty of Peace and Friendship between Japan and the People's Republic of China.
In 1949, from which the Communist Party of China which leads Mao Tse-tung controlled a continent and the People's Republic of China was formed and it Kuomintang Chiang Chieh-shih in the Republic of China escaped from to Taiwan, the Japan is still under the occupation of the GHQ, or admit any as legitimate government of China did not free will is given to Japan itself.
As for the San Francisco peace conference concerning the independence of Japan in 1951, too, because the delegacy in China was in the Republic of China and the People's Republic of China which, and in Union country, for the United States and the United Kingdom of opinion did not match, neither was invited it was supposed to devote pacification in Japan and China to the judgement in Japan after the independence.
However, for Japan which links the U.S. with an alliance by the Japan-U.S. Security Treaty and it have his name entered in a list of the liberal national group, it isn't possible at all to have diplomatic relations with the communism, and it chooses Taiwan to link Japan-Taiwan Peace Treaty among the Republic of China governments in Taiwan in next 1952, and so on, as the orthodox administration.
With this, it isn't possible to do the public contact with the side of the Chinese Communist Party and it stayed in the alternating current with the private level through Japan-China Friendship Association which was established in 1950 and so on.
The action to prohibit China-bound export completely, and so on, was taken from December of same year, and the Chinese Communist Party supported the North Korean side about the Korean War and had entered the war, too, and as for the toward communist China diplomacy, there was not developing under Yoshida Shigeru administration at all.