Purpose of this study is to clarify the evaluation of thermal comfort based on temperature differences between outdoor and indoor thermal conditions in summer. The experiments were performed to evaluate temperature difference between indoor and outdoor thermal conditions (29, 31, $33^{circ}$) by physiological and psychological responses of human. According to physiological responses, TSV (thermal sensation vote) and CSV (comfort sensation vote) and psychological responses, ECG (electrocardiogram), MST (mean skin temperature) of human, it was clear that the optimum temperature difference is about $5^{circ});and;7^{circ}$).