A model detection apparatus comprises a number of estimate parameter memories for storing mutually different distribution estimate parameters representing occurrences of input data. A number of distribution estimators are respectively associated with the parameter memories for producing distribution estimate parameters from data stored in the associated parameter memories and from a series of input data, and updating the associated parameter memories with the produced parameters. A model series memory stores candidate models corresponding in number to the parameter memories. A model series estimator produces candidate models using the series of input data, the stored distribution estimate parameters and the stored candidate models, and updates the model series memory with the produced candidate models. An optimal model series calculator calculates an optimal series of models from the candidate models stored in the model series memory.