The purpose of this research is to develope a pattern of apartment unit residence to reduce $CO_2$ applicable in architecture design, and based on economical efficiency analysis for an actual result. Patterns of apartment can be primarily divided into three types; a plan type, a block plan, a balcony type. First, we examine and analyze current research of energy saving of apartments. Next, we calculate construction cost by type followed by suggested design factors of apartment building, and overall evaluation is done by analyzing amount of energy consumption, $CO_2$ emission, running energy cost and life cycle cost. Based on the overall evaluation results, we finally suggest the $CO_2$ efficient plan type for apartment buildings.