A controller repeats an erase operation, an erase verify operation, and a step-up operation. A first storage unit stores a value of an erase start voltage applied first as an erase voltage when a series of erase operations are executed. A second storage unit stores a value of an erase completion voltage which is an erase voltage when erasure of data is finished in the erase operation and the erase verify operation. A first comparator compares the erase completion voltage with the erase start voltage each time the erase operation is executed. When the first comparator determines that the erase completion voltage is larger than the erase start voltage, a counter counts up a count value. When the count value becomes larger than a predetermined value, a second comparator updates a value of the erase start voltage stored in the first storage unit.