According to an embodiment, in a cache system, the sequence storage stores sequence data in association with each piece of data to be stored in the volatile cache memory in accordance with the number of pieces of data stored in the nonvolatile cache memory that have been unused for a longer period of time than the data stored in the volatile cache memory or the number of pieces of data stored in the nonvolatile cache memory that have been unused for a shorter period of time than the data stored in the volatile cache memory. The controller causes the first piece of data to be stored in the nonvolatile cache memory in a case where it can be determined that the first piece of data has been unused for a shorter period of time than any piece of the data stored in the nonvolatile cache memory.