A storage data reconstruction system including a plurality of storage units for storing therein divided data, the plural independent storage units forming a set; units for storing therein ECC data corresponding to the divided data; a spare storage unit for storing therein reconstructed data; an I/O-reconstruction control circuit; a timer; a data reconstructing table for a storage unit which is failed; and a circuit for reconstructing faulty data. When a failure occurs in any of the storage units, the failure is detected by an error check, a state of the failure is discriminated, a preferred processing suitable for the state of the failure is selected from a processing of a normal access or read/write and a data reconstruction processing, and the selected processing is carried out, or the frequency of the processing of the normal access or read/write and the data reconstruction processing, or the ratio of the amount of the data reconstruction processing within a unit time, is set. The time taken to reconstruct the faulty data does not exceed a fixed period of time.