A control circuit applies a write pulse voltage to a selected word line to perform a write operation to 1-page memory cells along the selected word line. The circuit then performs a verify read operation to confirm whether the data write to the 1-page memory cells is completed. According to the result of the verify read operation, a step-up operation is performed out to raise the write pulse voltage by a step-up voltage. The control circuit changes the amount of the step-up voltage according to a distribution width of a first threshold voltage distribution generated in process of the write operation to the memory cells.