This paper is considered on the possibility of social structure of TOSA port in the Middle Ages viewed from the restoration of the dug standing pillar buildings. The results are as follows. 1) There was thin concept on the individual ownership of land in TOSA port. 2) The population of residents in TOSA port was very much different by the seasons, because that it might be left during winter. 3) There were no standard courtesy spaces in TOSA port.
