The purpose of this study is to identify the characteristics of the thermal environment, and to analyze the relationship between the thermal reactions and the skin temperatures in the lying position in the radiant floor heating system. The results are as follows: 1) The globe temperature was nearly equal to the operative temperature in the room. 2) The floor surface temperature and the globe temperature were 26.4$^{circ}C$ and 23.6$^{circ}C$, respectively when the whole body temperature was at neutral point. 3) The mean temperature of the six skin parts was 31.3$^{circ}C$ (cold thermal environment); 34.1$^{circ}C$ (neutral thermal environment); 35.1$^{circ}C$ (hot thermal environment).