This paper investigates physiological effects of indoor greenery in a simulated office space as a result of subject experiments. Indoor greenery is expected to mitigate stress of occupants in an office space mainly due to the visual effect. However, the optimal green volume is unknown to recover from stress in an office. In order to investigate the optimal green volume, subject experiments are carried out in a simulated office room with greenery of 6 types of different green factors, including the control condition without a plant. As a result, the optimal green factor to mitigate stress is evaluated when the green factor is in the middle ratio for the dynamic visual field among 6 types of greenery layouts. The optimal green layout by the subject experiments is the same type as the inquiry survey previously submitted.