An upper system of an NVM device transmits, to the NVM device, a write command that designates a logical address, the write command being associated with an expiration date corresponding to a data expiration date correlated with write target data. The NVM device correlates an expiration date correlated with the write command with a logical address specified from the write command. The NVM device writes pieces of data of which the remaining time which is the time to an expiration date belongs to the same remaining time range to the same physical storage area among the plurality of physical storage areas. The NVM device erases data from a physical storage area when the expiration dates of all pieces of data in the physical storage area have expired.