A controller includes an identification information management table that manages identification information indicating, for each of addresses in second-management unit, whether one or more data in first management unit belonging to the addresses is stored in the second or the third storing area. When the controller executes a process of flushing data from the first storing area to the second storing area or the third storing area, the controller updates the identification information in the identification information management table. The controller executes a process of reading data from the second storing area or the third storing area by referring to the identification information. As a result, the speed of searches conducted in the management table is increased.