Depending on the region and timing, ancient Tombs were shown different between each other. It provides a very important clue that a society is comprehended by identifying structural characteristics and nature of buried artifact in the constructing Process. Especially, it’s important a careful analysis of the social environment and change process that the group have in order to study Deeply into the nature of the group that constructed. In this respect, it conducted research of the Yaksa-dong & Buk-dong ancient ruins that had been built in the Three Kingdoms period. The focuses are the circumstance of that time and the social, functional character that the group that constructed the ancient tombs. The tombs of the Three Kingdoms period in Yaksa-dong & Buk-dong ancient ruins were graveyard of regional groups that it had been constructed to last for nearly 350 years from the late fourth century of the first wooden chamber tomb to the late seventh century of the last stone room tomb. The iron manufacturing tools have feature that it’s buried during only certain period of time from the first quarter of fifth century to the second quarter of sixth century. It's time Silla pursuing most actively territorial expansion in the 5th and 6th centuries. Ulsan region had been taken bridgehead roles for Silla in the war especially on Gaya where located in downstream of Nakdong River. And It is at the excellent iron manufacturing centers called Dalcheon iron production complex adjacent to the site. When considered the above times, locational characteristics and certain artifacts named Iron manufacturing tools, it seems to the constructing group in Yaksa-dong & Buk-dong ancient tombs that the Metal worker group was in charge of production, distribution and supply of the Iron arms with a background of the excellent iron manufacturing centers called Dalcheon iron production complex for the Military defense, expansion force of Silla.