A means (35) for latching stored data is disposed outside an array of non-volatile memory cells (1). Before erasure of the memory cells (1), some of the stored data items in the non-volatile memory cells are transferred to and held in the latch means (35). The saved data items are written again after erasure, or alternatively, the data items transferred to the latch means (35) are used to determine certain designated regions in which erasure is inhibited. This enables the conservation of certain stored items, and thus, the prevention of illicit use. The shortening of testing time is also made compatible with the conservation.