In this paper, we propose indexing conference movies with thinking states. Currently, one of reasons why conference movies do not represent participants' thinking states is that existing ways do not place emphasis on recoding participants' concentration and interest. To address this issue, we define MS-Level (Mental State Level) derived from one's beta wave (a part of brainwave) as an indicator of depth of thinking, and index conference movies with MS-Index (Mental State Index). 3 experiments have been conducted to evaluate our proposition using a prototype system consisting of a movie player with MS-Indices. We conclude that our proposal will contribute to a better understanding of participants' thinking states during conferences, and users can find scenes in which participants think well or not.