An object is to achieve efficient shredding of recording media.For a storage system 10 which accepts a data input/output request transmitted in units of files from the client device 2 and includes a recording medium (hard disk drives 171) for storing in units of data blocks a file entity specified by the received data input/output request, in the information processing device (server device 3) performing data write or read, for shredding data blocks including a recording medium, from the files stored in the recording medium, a file whose update frequency exceeds the previously set threshold is selected and the selected entity file is stored in the data block to realize pseudo shredding for the data block.