The aim of present article is to make clear some obscurities of the ancient historical documents in Japan, especially Kojiki and Nihonshoki. In order to attain this purpose, we can fortunately nake use of the records in the Sung-shu 宋書. It is recorded that there had been diplomatic intercources between the Sung court and the Five Kings of ancicient Japan. Founded upon the critical survey of these records, this article ascribes to the following opinions. The first is that we can identify the King 讃 [tsan] with the Emperor Nintoku, 珍 [tïen], with Hanzei, 済 [tser] with Ingyo, 興 [hïəɓ] with Anko and 武 [muïɑɓ] with Yuryaku. In this regard it is noted that, so far as the genealogical order of Emperors is concerned, the accounts of Koliki and Nihonshoki are exceedingly, reliable. Secondly, we have tried to identify the anonymous Kings who dispatsched the envoys to the Sung court in 430, 460 and 477 A. D.. In this point we cannot agree with the accepted theory concerng the chronology of ancient kindom of Japan which had been established according to the reports in Kojiki and Nihon-shoki. But in Sung-shu we can also see the dates when they were recognised as the Japanese emperors by the Sung court. It seems to me that by this record we can guess their names. Thirdly, in the Sung-shu we can find the message of the King 武 which had been sent to the Sung emperor. In this message the King 武 shows the glorious lives and deeds of his ancestors. According to this description we have got an impression as if the King 武 and his ancestors had been heroes at the time of founding of Japanese Empire. But when we closely examine the texts, we must realize that the greater part of this message is mere copy of Chinese classical literatures. For example, the phrase "they conquered enemies all through the mountains and rivers so that they had no time to stay at home" "躬擐甲冑,険跋渉山川,不遑寧処" is the conventionary expression which was usually found in Tso-chuan 左伝 and Mao-shin 毛詩. Accordingly we can not accept the description of this message as the real historical facts. The result is that we must modiby the accepted image of the the age of heroes in early history of Japan.