A data processing apparatus which saves data in a volatile memory into a nonvolatile memory when power is off, the data processing apparatus including: a detecting circuit for outputting: a momentary interruption detecting signal when a power source voltage is below a first threshold voltage, and a power failure detecting signal when the power source voltage is below a second threshold voltage that is lower than the first threshold voltage; and a control section adapted to start saving of the data in the volatile memory into the nonvolatile memory when the detecting circuit has output the momentary interruption detecting signal, continue save of the data, and carry out a predetermined shutdown processing when the detecting circuit has output the power failure detecting signal after the detecting circuit has output the momentary interruption detecting signal.