An encryption key used with a storing apparatus and an encryption key used with a non-volatile cache memory are identical to each other. A cache control portion unit effects control in such a way that an encryption key EK used to encrypt first data stored in the storing apparatuses, and an encryption key EK used to encrypt second data which are data corresponding to the first data and are stored in the non-volatile cache memory, are identical to each other. If the cache control portion receives a write request and first data WD, the cache control portion identifies from the storing apparatuses a storing apparatus that is to be the storage destination of the first data, identifies an encryption key allocated to the identified storing apparatus, encrypts the second data corresponding to the first data using the identified encryption key, and stores the data in the non-volatile cache memory.