A first decision process, which reads data from a memory cell under a first deciding condition to decide pass/fail and applies a signal to the memory cell to change an amount of charge stored in the memory cell if the data is decided as fail, and a second decision process, which reads the data from the memory cell under a second deciding condition that is relaxed rather than the first deciding condition to decide the pass/fail, are executed, and then the processes are repeated from the first decision process when the data is decided as fail in the second decision process.