PLANT MONITORING SYSTEM, PLANT MONITORING METHOD, AND PROGRAM STORAGE MEDIUM

In one embodiment, a plant monitoring system includes a threshold acquiring module (7), a judging module (93), and a warning module (10). The threshold acquiring module (7) acquires in advance, based on a value obtained by leveling the dispersion in first process values corresponding to output values at a first point in a monitoring object and a value representing the dispersion, first thresholds representing a first range of the dispersion in the first process values and second thresholds representing a second range. The judging module (93) compares the first process values chronologically acquired based on the output values at the first point with the corresponding first thresholds and second thresholds. The warning module (10) creates alert information containing information on at least a time point when the first process value exceeds one of the first thresholds and the second thresholds.