A data center includes an air-conditioned room, two rack rows formed on a floor surface of the air-conditioned room and each composed of a plurality of racks arranged in a horizontal direction, each of the plurality of racks housing electronic devices in multistage configuration, an air conditioner for conditioning air in the air-conditioned room to eliminate heat generated from the electronic devices housed in the plurality of racks, and a hot zone in the air-conditioned room. The hot zone is defined by the two rack rows arranged on the floor surface of the air-conditioned room such that rear sides thereof are opposite each other at a distance, a ceiling disposed above the two rack rows, two panels disposed at both ends of the two rack rows in the horizontal direction and extending from a lower end of the two rack rows to the ceiling, and two partitions disposed at an upper front top end of the two rack rows and extending to the ceiling. The ceiling includes an exhaust port for discharging heat in the hot zone, and the air conditioner is operable to introduce air-conditioned air from the air-conditioned room through front sides and then the rear sides of the two rack rows into the hot zone. The data center further includes a heat recovery means for recovering a heat of the air discharged through the exhaust port from the hot zone before cooling down the air by the air conditioner.