PURPOSE: To facilitate construction work, at the same time, require no strict accuracy for level adjustment of the arrangement surface and to effectively prevent the occurrence of an unnecessary space easy to occur in a butt section of drainage members adjacent to the longitudinal direction.

CONSTITUTION: Joint projections are formed on one of both longitudinal ends of drainage members 1 formed of synthetic resin foamed particle molding bodies obtained by an in-mold molding method so that a linked space is formed between foamed particles, and joint recesses corresponding to the joint projections are formed on the other of them. Both ends are fitted to each other to connect the adjacent drainage members 1, and a plurality of drainage members 1, 1, 1,... are linked in the longitudinal direction. When they are overlapped in both up and down stage, a drainage gutter 2 is formed in the central part in the direction of the width of the drainage members 1 so that a hollow channel 3 running through a longitudinal direction of the drainage members 1 is formed inside them.