A semiconductor integrated circuit including a nonvolatile memory cell is provided with a detection/word line voltage control circuit for sequentially supplying two or more mutually different unstable bit detecting voltages to a control gate of the nonvolatile memory cell to cause the nonvolatile memory cell to output a plurality of pieces of readout data, and an OK/NG determination circuit for comparing the plurality of pieces of readout data to determine whether the nonvolatile memory cell is stable or not.