A non-volatile storage device comprises non-volatile memories for storing data; and a memory controller for carrying out control of the non-volatile memory. The memory controller stores second error correcting code as well as first error correcting code stored in the same page of the data. The memory controller, when writing data smaller than a predefined size, does not add the second error correcting code, and stores duplexed data of the data and the first correcting code in a different page. The memory controller, when reading, corrects data using the first and/or second correcting code. The valid data management table manages which logical block stores valid data with respect to an identical logical address.