Grasping subtle differences in human mental state reflected in subjective statements is important to precisely evaluate environmental conditions in which occupants express various feelings such as satisfaction and pleasure. The purpose of this study is to propose and assess a word-choice method for grasping precisely the human mental state in the evaluation. The conventional rating-scale method and the proposed word-choice method are compared by means of a series of experiments on thermal evaluation. Results of the study showed that the words used in the thermal evaluation were distinguished in terms of not only thermal sensation but also comfort, and that the word-choice method would be effective for expressing differences in human mental state.