A light stability testing device for conducting an accurate light stability test that permits an accurate ultraviolet irradiation and an accurate visible light irradiation, the device comprising an optical sensor having a visible light measuring sensor (5) for measuring the dose of visible light, and a ultraviolet measuring sensor (6) for measuring the dose of ultraviolet ray, an optical system having a total light regulating means (331) for regulating the absolute quantity of light emitted from a light source and a ultraviolet ray regulating means (335) for regulating the dose of ultraviolet ray in light regulated by the total light regulating means, and a control unit for controlling a total light control unit that controls the total light regulating means (331) by a signal from a visible light measuring sensor (5), and the ultraviolet ray regulating means (335) by a signal from the ultraviolet measuring sensor (6). <IMAGE>
LIGHT STABILITY TESTING DEVICE