A control unit included in a PLC generates power-cut retaining information to be retained at a power cut, and stores the generated power-cut retaining information into a main memory. The control unit includes a file system unit for reading and writing target information from and into a nonvolatile memory. When the file system unit receives a power cut notification indicating a cut of power fed while reading or writing target information from or into a nonvolatile memory, the file system unit stops the reading or writing process, and writes the power-cut retaining information stored in the main memory into the nonvolatile memory using power fed from the auxiliary power supply.