In this study, we reproduced the sequential decision-making method for specification changes and observed the differences between Waterfall and Agile development. Then, we created Waterfall and Agile models, and used reinforcement learning to learn the decision of "should specification changes be made?" when user needs changes. As a result of observing the differences in decision-making methods obtained after learning, the Waterfall model tended to make specification changes in the latter half of the development process and to accept them less frequently. Alternatively, in the Agile method, specification changes were made in the first half of the development process, and the number of the acceptance tended to be high. This suggests that it is necessary to change how to make specification changes depending on the development method.