First and second units are mounted on a rear side of a housing of a storage system. Either of the first and second units includes a fan. The rear side of the housing includes an upper-tier portion defining an upper-tier opening, and a lower-tier portion defining a lower-tier opening, and the housing further includes a boundary portion that is a boundary between the upper-tier portion and the lower-tier portion, and a shutter unit. The boundary portion includes a first through hole that is a through hole connecting an upper-tier passage and a lower-tier passage. When the fan is operating, if the first unit is removed from the upper-tier portion, the shutter unit blocks the upper-tier passage, and if the second unit is removed from the lower-tier portion, the shutter unit blocks the lower-tier passage.