There is provided a novel storage system in which the number of signal lines will not increase even if the number of storage devices to be connected in a RAID system increases, and a novel data transfer method to enable a high-speed data transfer even when the transfer rate of the IDE device side is low. A RAID system (10) which is a storage system in which a RAID controller (11) connected to an ATA host and a plurality of IDE devices (12A to 12D, and 22A to 22D) are connected by an IDE bus, characterized in that at least two or more IDE devices are connected to one channel of the IDE bus and said RAID controller and each of said IDE devices are connected by a common data bus and a common address bus within the same channel.