This study aims at examining the background and development process of Masan city after Koryo Dynasty, making a reconstructive map of Original Masan using the first registration maps made in 1912 and analyzing the urban structure of the Original Masan area. The origin of Masan city went back to Koryo dynasty. Around 1040 Koryo government placed an official shipping facility in Masan to transport the taxed grain to the capital city. After that Masan became an important port covering the southern part of KyungSang-Do. And the urbanization of the Original Masan began to bud after a shipping facility was again established by the Chosun Dynasty in 1760 and strengthened in the 19th century after the social standing system was broken and many peasants moved to cities as daily workers. In 1899 Masan was forced to be opened to foreign powers and they placed an international settlement distanced from the area(Original Masan). After this many Japanese advanced to the international settlement and further to the area. The advancement of Japanese brought a critical change in the urban structure of the area. Land was owned by Japanese and many modern sysytems were introduced such as modern buildings, new roads, railroad and modern factories. According to the reconstructive map of the area, 80.5% of land lots are less than $200m^2$ showing the size of each land lot is comparatively small. And Japanese occupied 31.5% of the land in the area. Their land was located on the stratigic points near the port and the center of commerce. The ratio of the road area to the whole land was around 14%, not so low for urban areas in that time. The reconstructive map reveals the exact coastline of the year 1912 erased now due to filling the sea and extending the land, Present Masan city has been developed having the Original Masan as its nucleus. The area has been always the center of urban activities for Masan city. Making an exact reconstructive map for the area and analyzing the urban structure of the area in 1912 is a very important work to understand Masan city wholy.