PURPOSE: To enhance system reliability by outputting abnormality information while taking account of comparison with a previous measurement and rising rate of measurement thereby preventing overissue of confusing information.

CONSTITUTION: Data sampled through a loop of a sensor 1-a channel switch 2-an A/D converter 3-an average value operating circuit 4-a personal computor 5 is subjected to a tendency management. The personal computor 5 compares an average value data of once/Hr with a threshold value. In case of an abnormal value, a frequency analysis data is inputted automatically to the personal computor 5 through a loop of the sensor 1-the switch 2-a frequency analyzer 7-the personal computor 5. Automatic diagnosis program in the personal computor 5 is then started and content of abnormality is outputted automatically on a printer 6. Such a decision is made that the information is abnormal, when an abnormal value a1 satisfies following formula. ai>ai-p, ai-q, and ((ai-ai-p)-(ai-p-ai-q))>1, where ai represents an abnormal value in current measurement and ai-d, ai-q represent abnormal values in previous and two times eariler measurements, respectively, and (p, q=1, 2,..., q>p).