A process state monitoring device, comprising: a component separation computation unit configured to separate two or more components from time series data of a value indicating a state of a process, wherein the process is one of a manufacturing process, a power generation process, a conveyance process, and a waste liquid treatment process; a characteristic value computation unit configured to compute a statistic based characteristic value from each component separated by the component separation computation unit; a state determination unit configured to classify the state of the process on the basis of the characteristic values computed by the characteristic value computation unit; the process state monitoring device being characterized by further comprising: a similar case search unit configured to: search a past database for an operation case similar to the process on the basis of the characteristic values computed by the characteristic value computation unit, determine a similarity of characteristic values computed by the characteristic value computation unit and characteristic values of each operation case on the basis of a distance or an angle in a variable space composed of a plurality of characteristic values in accordance with the number of characteristic values to be compared; and compute, as a contribution, the component contributing to the similarity. a component separation computation unit configured to separate two or more components from time series data of a value indicating a state of a process, wherein the process is one of a manufacturing process, a power generation process, a conveyance process, and a waste liquid treatment process; a characteristic value computation unit configured to compute a statistic based characteristic value from each component separated by the component separation computation unit; a state determination unit configured to classify the state of the process on the basis of the characteristic values computed by the characteristic value computation unit; the process state monitoring device being characterized by further comprising: a similar case search unit configured to: search a past database for an operation case similar to the process on the basis of the characteristic values computed by the characteristic value computation unit, determine a similarity of characteristic values computed by the characteristic value computation unit and characteristic values of each operation case on the basis of a distance or an angle in a variable space composed of a plurality of characteristic values in accordance with the number of characteristic values to be compared; and compute, as a contribution, the component contributing to the similarity. search a past database for an operation case similar to the process on the basis of the characteristic values computed by the characteristic value computation unit, determine a similarity of characteristic values computed by the characteristic value computation unit and characteristic values of each operation case on the basis of a distance or an angle in a variable space composed of a plurality of characteristic values in accordance with the number of characteristic values to be compared; and compute, as a contribution, the component contributing to the similarity.