For the department store building, less windows give less load for amount of solar radiance but excessive load of indoor human physical heat and lighting which causes the excessive generation of air conditioning load even at the change of seasons in Spring or Fall. Thus, for the department store building, the effect of free cooling is expected by changing the indoor/outdoor air for the air conditioning load which generates at the change of seasons, but the sufficient ventilation effect is not expected because the installation area of opening facing to the outside. Therefore, we installed the ventilation inlet on the lower floor and the outlet on the upper floor and analyzed the free cooling effect using the escalator zone as a ventilation path. We used the analysis program IES/VE to calculate the air conditioning load and analyzed the natural ventilation amount using a STAR-CCM+. As a result of that, we to reduce the energy savings in cooling load from October to may to buoyancy in natural ventilation, the exchange of indoor and outdoor air to partially in mechanical ventilation may achieve energy savings in June and September. In the case of the department store under natural ventilation system, a cooling load can be reduced by a natural ventilation system from Oct. to May, and an additional mechanical ventilation system is needed from Jun. to Sept.