This study is about the cost estimation of an apartment housing in new project and analyzed the actual project cost that has been classified according to the work types as the room costs from historical data. It was conducted to present utilization of the findings from the analysis. To do this, a systematic analysis for the room costs was established, and conducted comparison analysis for room costs for apartment buildings of 3 different construction firms. The results made out from this study can be summarized as follows: 1) It has presented systematic classification of room costs estimation for the work type project cost and established a system for room costs by analyzing performance statement, 2) and actual costs for room costs derived from 6 different case studies of 3 construction firms were analyzed to help finding out similar-scaled costs differences in terms of respective to proportional room costs. 3) The estimation of room costs suggested in this study can be utilized for the outsourcing and materials management according to the cost estimation of an apartment housing in new project and the degree of building progress.