When a special write command from a host is executed, switching is performed so that the data designated by the command will not be input to an ECC generator. In accordance with an erasure pointer setting command from the host, a programmable erasure pointer generator sets, in an erasure pointer memory, a special erasure pointer that indicates, as an error location, the location designated by the setting command. This pointer is used for erasure correction performed when the data written to a disk by the execution of the special write command is read in accordance with a normal read command.