A computer-implemented monitoring device (1, 10) comprising: model generation means for dividing time-series information from among pieces of time-series information obtained by associating pieces of information of a plurality of items related to a plant or facility to be monitored on a time-series basis over a predetermined period, the time-series information associated with each item to be modeled, into pieces of divided information of periods, each period shorter than the predetermined period, and generating models representing correlations related to the pieces of divided information; and determination means for, by applying another time-series information obtained by associating the pieces of information of the plurality of items on a time-series basis during a period different from the predetermined period, to at least two or more of the models related to the each item, for each of the two or more of the models, determining whether the correlation represented by at least one or more of the models is maintained, and performing a determination related to the each item based on results of the determining, wherein the model generation means is configured to divide the time-series information associated with the each item, on the basis of a plurality of division conditions, and to generate the models related to the pieces of divided time-series information, characterised in that the model generation means is configured to: obtain a total amount of change in parameters between the generated models related to pieces of divided time-series information, combine the pieces of divided time-series information, for which the obtained total amount of change in parameters satisfies a predetermined condition, and regenerate models related to the combined pieces of divided time-series information. model generation means for dividing time-series information from among pieces of time-series information obtained by associating pieces of information of a plurality of items related to a plant or facility to be monitored on a time-series basis over a predetermined period, the time-series information associated with each item to be modeled, into pieces of divided information of periods, each period shorter than the predetermined period, and generating models representing correlations related to the pieces of divided information; and determination means for, by applying another time-series information obtained by associating the pieces of information of the plurality of items on a time-series basis during a period different from the predetermined period, to at least two or more of the models related to the each item, for each of the two or more of the models, determining whether the correlation represented by at least one or more of the models is maintained, and performing a determination related to the each item based on results of the determining, wherein the model generation means is configured to divide the time-series information associated with the each item, on the basis of a plurality of division conditions, and to generate the models related to the pieces of divided time-series information, characterised in that the model generation means is configured to: obtain a total amount of change in parameters between the generated models related to pieces of divided time-series information, combine the pieces of divided time-series information, for which the obtained total amount of change in parameters satisfies a predetermined condition, and regenerate models related to the combined pieces of divided time-series information.