PURPOSE: To clarify a series of flows in an abnormal condition by freezing log information at respective time points only for the prescribed number of times for a prescribed time set in accordance with the detection of the abnormality generation of a system and taking it out to the external part.

CONSTITUTION: When an abnormality occurs at a system, it is detected by an abnormal condition detecting circuit 1 and a log out instruction is executed from a log out time interval setting circuit 7 to a log out frequency setting circuit 8 for a setting time interval in accordance with this. Each time the circuit 8 receives the log out designation, the number of the times of the instruction is counted up and it is judged whether or not the accumulation is larger than the prescribed value. As the result of judgement, a log out instruction is communicated to a freezing control circuit 9 at the time of the set value or below. The freezing releasing of the log information is instructed from the circuit 9 to a freezing circuit 2 in accordance with it and the freezing is released. Simultaneously, a storing area is instructed to a floppy disk control circuit 4 by the circuit 8 and the log information sampled by a log out circuit 3 is stored by the circuit 4.