A complex system where a plant group having a heat island phenomenon suppression effect and a solar cell having a carbon dioxide generation suppression effect are installed together. The purposes are to eliminate an adverse influence of both shadows of the plant group and the solar cell and to prevent the solar cell system from flying away by the wind pressure against the base side. The average height of the solar cell module is greater than that of the plant group. The plant group and the solar cell module are installed with a gap larger than the distance corresponding to the height difference between them. At least between the paired plant group and solar cell which face each other, an area for a person to walk through is provided. More than half of the ventilation area of the base side is covered with the plant group, a heat insulating material, and a moisture-retaining material.