AREX (Incheon Airport Railway Express) operates trains between Seoul and Incheon Airport. One type of trains stops on every 10 stations, and another only on the two end-stations which called an Express train. The passengers traveled on express trains are very small since there are only two stops, Seoul and Incheon Airport Stations. The passengers of express trains will be more attracted if the express train stops on the intermediate stops (Gimpo station) since Line #9 and Line #5 are connected to from Gangnam. An on-board survey was conducted to predict the potential demand in case the express train stops at the Gimpo station. Further the costs required to improve platforms of the station were estimated to figure out the economic feasibility against the demand increases. It analyzed 938 increases for the case of intermediate stopping on the same travel time condition and 1,299 increases for the case of extra stop with decreased travel time. The study concluded the latter case appears desirable in the stance of long-term while both cases are economically feasible.