To provide a disk array system which particularly enables the use of a WORM function when the disk array system uses RAID. When receiving a write request from a computer (100), it is judged whether or not a writing of write data from the computer is possible, based on a content indicated by write inhibition information. If the writing is possible, the guarantee code of the transferred data is generated, the write inhibition information indicating that a region in which the data is stored is not writable is generated, and the generated write inhibition information is stored in the guarantee code, the guarantee code storing the write inhibition information is assigned to the region in which the data received from the computer (100) is stored, and the data to which the guarantee code storing the write inhibition information is assigned is stored in a cache memory (230) and/or a disk drive (270). If the write data from the computer (100) is not writable, it is informed to the computer (100).