A storage controller of the present invention reduces maintenance work by the user by irreplaceably mounting the respective component parts inside an enclosure. A plurality of disk drives, which comprise a spare drive, and repair slots are arranged in close proximity in a matrix on the front side inside the enclosure. A backboard is disposed rearward of the respective disk drives. A plurality of control boards are arranged rearward of the backboard by being stacked one atop the other. A plurality of disk drives and a plurality of batteries respectively stacked one atop the other are arranged on the one side of the respective control boards. A plurality of power devices stacked one atop the other are arranged on the other side of the respective control boards. A plurality of cooling fans are arranged in the center part of the enclosure. The respective parts are affixed to the enclosure so as to be irreplaceable under normal circumstances.