A data center includes a first rack, a second rack, a supply duct provided over a first space between the first and second rack, a first circulation duct including a first suction port disposed at an end side of the first rack and a first exhaust port disposed at the first space side and provided between an upper portion of the first rack and the supply duct so as to close up the first space, a second circulation duct including a second suction port disposed at an end side of the second rack and a second exhaust port disposed at the first space side and provided between an upper portion of the second rack and the supply duct so as to close up the first space, a first and second barrier that closes up the first space at one and the other end of the first and second rack, respectively.