To provide a nonvolatile semiconductor storage device and a drive method thereof capable of preventing lowering efficiency of write or erase operation and reducing the write time and the erase time. [MEANS FOR SOLVING PROBLEMS] A nonvolatile semiconductor storage device includes an electrically rewritable memory cell formed by a floating gate and a control gate layered on a semiconductor layer. The nonvolatile semiconductor storage device applies a plurality of threshold value fluctuation pulses having a stepwise high potential to the memory cell and then detects a threshold value of the memory cell. When the threshold value of the memory cell is not a predetermined value, a plurality of threshold value fluctuation pulses having stepwise high potential are applied to the memory cell from a potential of the lastly applied threshold value fluctuation pulse, among the plurality of threshold value fluctuation pulses, to which a certain potential is added.