A storage controller of the present invention can input and output data even when the track size, which is the host management unit, is not consistent with the block size of the storage device. A boundary correction unit adds gap data corresponding to a gap size to data in a buffer memory so that the boundary of the track and boundary of the block inside the storage device match. A guarantee code is added to each logical block received from the host, and these guarantee code-appended blocks are stored in a cache memory. By providing a gap in the storage device every 116 extended logical blocks, the start position of the lead block of a track matches up with the start position of the logical blocks of the storage device.