A measurement value judgment method for comparing measurement values from sensors provided at various locations of a system with pre-set reference values, and judging, based on the results of the comparison so made, whether the system is normal or abnormal, comprises the steps of judging a quantity of state relative to the load on the system and changing the reference values in response to the results of the judgement, the thereby judging accurately whether or not the system and sensors are in an abnormal status by accurately identifying the operating state of the system.