In the present research, we investigated the changes and individual differences of physical traits among the old people through physical function data and BMI (Body Mass Index) data of Japanese longitudinal study by using latent curve models. We first estimated the mean change patterns of physical traits, showing that in physical function moderate decrease was observed on average while female showed more rapid decrease. In BMI, female averagely indicated larger values than male but showed almost the similar change pattern to male. Individual differences of these changes were shown to be related to demographic variables, psychological variables, life-style variables such as smoking habits and other physical traits including eyesight. Additionally, longitudinal relationship was investigated between physical function and BMI, indicating the possibility that physical function may control rapid decreases of BMI in the old people. Finally, we attempted to extract multiple change patterns hidden in the whole data. As a result, two main classes were extracted whose change patterns were different in its intercepts and slopes. All analyses were conducted by Bayes estimation based on MCMC (Markov Chain Monte Carlo) method, and we showed the all program codes of WinBUGS in the Appendix.