Human thermal sense is not expressed only by simple heat equilibrium. The influence of visual and auditory stimuli causes differences in overall thermal sense arrived at by sophisticated sensory processing by the cerebrum. If it can be clearly shown that a thermal environment considered slightly uncomfortable could be ameliorated using visual stimuli, the cost effectiveness of such an initiative would be highly significant, particularly in terms of air conditioning system running costs. Focusing on the visual stimuli provided by greenery, experiments were conducted in a thermal environment deemed slightly uncomfortable, where the temperature was set at a base point of 28ºC. Experiments were conducted in a temperature-controlled room. Thermal environmental conditions were set at three different temperatures: 25ºC, 28ºC and 31ºC. Wall surface temperatures were set to equal these temperatures. Air velocity (calm air currents of 0.2 m/s or less) and relative humidity (60% RH) were set the same throughout. Subjects were asked to sit quietly for the test. The visual stimuli consisted of ten different types of scenery, including that of leafy vegetation. The influence of overall stimuli of the cerebrum on the indoor thermal environmental index ETF was determined to prove the significance of actively placing visual stimuli in spaces. Thermal stimuli influence the human body on mean skin temperatures, while visual stimuli do not affect mean skin temperatures. In ETF deemed fairly uncomfortable, that is at a range of hotter than 28-29ºC, clear improvements were observed in thermal sense due to the influence of visual stimuli such as natural elements including vegetation like greenery. Visual stimuli were appropriate at a level of up to 69% greenery, where a dynamic effect on warmer environmental conditions can be felt and where the depth of fuller vegetation cover can be perceived.