PURPOSE: To prevent the destruction of content of processing program due to initial program load processing, by transferring a controlling junction to a filure processing program and automatically shunting the processing program to an auxiliary storage device, if a loop state takes place.

CONSTITUTION: If a loop state takes place during data processing, an actual execution requiring time exceeds a time value set to a watchdog timer 4-1 and the time- over is detected by it. When this time-over is detected, an interruption is given to a failure processing program 3. The program 3 checks the cause to the said interruption and judges that the said interruption is caused by the production of loop state. Based on the said judgement, a processing program 2 is shunted to an auxiliary storage device 5.