A data buffer control unit obtains data from a cache according to a command retained in a command queue retaining a command(s) for reading data from the cache, and a magic ID generation circuit generates a magic ID. The data buffer control unit assigns the data obtained from the cache with the magic ID, writes the assigned data to a data buffer, and returns the magic ID to the command queue. When the data buffer control unit receives a read request and the magic ID which is returned to the command queue, it reads the data, which corresponds to the read request, from the command queue and compares the magic ID assigned in the read data and the received magic ID. If the two magic IDs compared by the data buffer control unit are not identical, a packet generator detects an error and reports the error to a host.