Plant diagnosis device

In a nuclear plant diagnosis device, there are prepared a mathematical model (single mathematical model) on every block put between measuring points of a plant and a combined mathematical model comprising blocks in adjacent with each other as one mathematical model. Measured values corresponding to each of the mathematical models are inputted, and estimated values on the output side obtained from the models and actually measured values on the output side are compared successively. The abnormalities of the plant are judged separately as to whether they are physical abnormalities or abnormalities in measuring system based on the pattern (combination) of the results of comparison. Since abnormalities in the measuring system and abnormalities in the plant physical system can be separately judged by the diagnosis of the data during plant operation, restoration treatment upon occurrence of an abnormality can be cope with rapidly. In addition, information for determining the capability of the operation of the plant can be provided. (N.H.)