Summary: The author presents an efficient method of analyzing an interest-rate model using a new approach called ’data augmentation Bayesian forecasting.’ First, a dynamic linear model estimation was constructed with a hierarchically-incorporated model. Next, an observational replication was generated based on the one-step forecast distribution derived from the model. A Markov-chain Monte Carlo sampling method was conducted on it as a new observation and unknown parameters were estimated. At that time, the EM algorithm was applied to establish initial values of unknown parameters while the ’quasi Bayes factor’ was used to appreciate parameter candidates. ’Data augmentation Bayesian forecasting’ is a method of evaluating the transition and history of ’future,’ ’present’ and ’past’ of an arbitrary stochastic process by which an appropriate evaluation is conducted based on the probability measure that has been sequentially modified with additional information. It would be possible to use future prediction results for modifying the model to grasp the present state or re-evaluate the past state. It would be also possible to raise the degree of precision in predicting the future through the modification of the present and the past. Thus, ’data augmentation Bayesian forecasting’ is applicable not only in the field of financial data analysis but also in forecasting and controlling the stochastic process.