In recent years, people have become increasingly aware of the importance of reducing power consumption by setting higher temperature of air conditioners. However, many people feel uncomfortable with higher room temperature. So it is important to analyze thermal comfort for making comfortable environment and energy saving. In this paper, we describe the measurement of brain activity during changing in a room temperature by near-infrared spectroscopy (NIRS). In our experiments, we measured oxyHb in prefrontal cortex by NIRS during adjusting the room temperature. The results show that oxyHb tended to increase during rise the room temperature, and oxyHb tended to decrease during lowering the room temperature. The results also show that oxyHb changed with the result of Predicted Mean Vote (PMV).