A non-volatile semiconductor memory apparatus and a data erasing method thereof are provided to suppress deterioration in reliability due to data rewriting. An erasing method of a flash memory is provided, which includes the following steps. A control gate is maintained at 0V, a high-voltage erase pulse is applied to a P well, such that electrons is emitted from a floating gate to the P well. Then, the control gate is again maintained, and a weak erase pulse with a voltage lower than the erase pulse is applied to the P well.