To reduce the construction cost by removing only the artificial lawn installed on the existing outdoor and roof-top courts, installing a synthetic resin cushioning material comprising a number of void parts and having the water permeability, on an upper face part of an exposed permeable asphalt concrete, and installing a new artificial lawn on the synthetic resin cushioning material.

In an existing outdoor court (A) where an artificial lawn (S) is installed on an upper face part of a water permeable asphalt concrete 3, the artificial lawn (S) forming the existing outdoor court A is removed, a synthetic resin cushioning material (a) is installed on an upper face part of an exposed water permeable asphalt concrete 3, and a new artificial lawn (S) is installed on the synthetic resin cushioning material (a). This synthetic cushioning material (a) is manufactured by coating a surface of a fine string material 1 with an urethane base resin liquid, and compress working the fine string material 1 to form a number of void parts 2 and to obtain the water permeability. A specific amount of the sand, the fine gravel, the powder of rubber chips, the plastic powder and the powder of glass scrap is scattered in the void parts 2 as a simple substance or a mixture thereof.