The controlled thermal environments in enclosed space during natural convection, such as a reefer hold of refrigerating cargo ship, are unnegligibly affected by thermal radiation. The quantity of heat transfer by thermal radiation depends upon surface temperature, emissivity and geometric configuration factor of surrounding walls. In order to investigate the effects of heat radiation to thermal environment, the radiative flux and heat flow between surrounding walls are measured in an air conditioned chamber installed a wall with lusterless black surface during allowing to warm or cool. Further, three dimensional analyses of heat transfer taking account of heat radiation are carried out for the model of the chamber used for measurements and the results of theory and experiment are compared. The relations between the emissivity of surface and the heat radiative flux or the distribution of air temperature in enclosed space are clarified by the results of calculation.