To provide a nonvolatile semiconductor storage device which can detect deterioration states of characteristics of memory cells for individual blocks of a flash memory, and can set an operation condition of the flash memory according to the deterioration states of the individual blocks.

When a block in a flash memory 20 is programmed, first time period (verification pass time of N% of memory cell) from the start of the program until N% (N is an arbitrary number of 1-100) of memory cell out of memory cells to be programmed in the block passes program verification is measured, when the first time period is lower than a predetermined determination reference value, a block address of the block is stored, when the block is accessed, operation condition of the flash memory 20 is changed to a predetermined operation condition.