In a nonvolatile memory device of the present application, when data of each write unit is read from a nonvolatile memory, an all-clear detector detects whether the read data is already cleared, and a control portion judges whether a flag is already written into a written flag area of the data that has been descrambled by a descrambler and then corrected by an error detection and correction portion. Using a scramble pattern that is generated by a scramble pattern generator and corresponds to the written flag area, a predetermined bit pattern is scrambled to a state that differs from the cleared state.