PURPOSE: To secure at least normal operating conditions even when a noise which cannot be checked by a noise preventing means invades by making a CPU execute a save routine when a noise is detected by a noise detecting circuit.

CONSTITUTION: Under a normal condition where no noises are received from both outside and inside, a prescribed program is normally executed at a data processing system 10. When a noise which affects the operation of the system 10 invades into some place of the system 10, the noise is detected by a noise detecting circuit 30 and its detect output NS operates an address switching circuit 34. Then a CPU12 is forcedly jumped to a specified address immediately and executes a prescribed save routine. By executing the save routine, the CPU12 is not set to a malfunctioning condition and can be restored to a normal controlling condition.