To improve thermal efficiency by a method wherein a panel body is constructed of a pipe for circulation of warm water, a baseboard provided with guide grooves for laying the pipe therein, and a rubber cushioning member laid on the baseboard.

A rubber cushioning member 2 is provided, and a baseboard 3 provided with a guide groove 7 in a U-shaped section composed of long grooves 7a and archlike grooves 7b is laid at the underside of the rubber cushioning member 2. Then, metal layers 5 and 6 serving as radiators for covering a warm water pipe to be laid in the guide groove 7 at the baseboard 3 are laid integrally in layers between the baseboard 3 and the cushioning member 2, and thereby a panel body 10 is formed. A tatami facing 1 is laid on the panel body 10. Therefore, thermal conductivity is improved for warm water circulating in the pipe while heat dispersion by the warm water can be prevented.