In this study we analysed the degree of psychological comfort in order to more accurately evaluate the alleviating effects of roadside planting on noise perception. It is widely known that alpha waves emerge when a person is under relaxing conditions. The alleviating effects were confirmed by studying the situation in which this type of alpha waves had emerged. Measurement of alpha waves was conducted in accordance with the ten-twenty electrode system with noise and video images of roadside planting having different amounts of green used as stimula. The results are as follows:(1) The analysis indicated that an increased amount of green closely relates to the generation of relaxing conditions because alpha2 waves increased as the amount of green increased.(2) It was confirmed that the roadside planting effectively affects the reduction of perceivable noise.(3) The noise perception is alleviated by the roadside planting covers the cars.(4) The alleviating effects of roadside planting, with flowers, on perceivable noise is higher than onlygreens.