Upon receiving an erase command and a first logical address, a controller in a first mode sets, as an erasure waiting area, an erasure unit area assigned with a first physical address associated with the first logical address in a first table. The controller in the first mode replaces, in the first table, the first physical address with a physical address assigned to an erasure completion area. The controller in a second mode sets the erasure waiting area as the erasure completion area. Upon receiving a release command to release the second mode at some point in time of data erasure from the erasure waiting area, the controller changes the operation mode to a third mode. The controller operating in the third mode erases un-erased data from the erasure waiting area and changes the operation mode from the third mode to the first mode.