A plurality of fluorescent lamps (30, 30 and so on) are disposed so as to be unevenly distributed in the periphery of an upper space above and opposing a sample placing surface (21) in an environmental test room (11). The irradiance distribution of the light from the fluorescent lamps (30, 30 and so on) on the sample placing surface (21) is set to be within the range of ± 25% with respect to the irradiance at the center of the sample placing surface (21).
