The research analyzed the distribution of the indoor temperatures of a radiant floor cooling system through mock-up experiments. It investigated the temperature difference of feed water, the vertical temperature difference of indoor air, the temperature difference of floor surface, and so on. The following is the results of the research. First, the research shows that the difference between indoor temperature and outside temperature was the smallest when the temperature of feed water was set at 16$^{circ}C$. In addition, the temperature changes according to indoor positions (wall, room, floor, and ceiling) were the most uniform. Thus, the research found that the cold water temperature of 16$^{circ}C$ is the most proper. In addition, it confirmed that the feed water temperature of 18$^{circ}C$ is effective because the temperature can lower the temperature of a room to 13.55$^{circ}C$, which is lower than the temperature of a non-cooling mode. Second, an investigation on the temperature distribution of vertical air in indoor space shows that the temperature distribution had a difference of 0.2 to 1.9$^{circ}C$ on the average, which satisfies the range of 3.0$^{circ}C$ in the standard of ISO.