Method of an apparatus for weather resistance test

In a weather resistance test, a process for washing the surface of samples (6) with a cleaning agent using spray nozzles (11a,11b) is added at least between the condensing of the dew on the surface (6) of the sample by a humidifier (9) after ultraviolet radiation from a source (1) has been applied and again applying ultraviolet radiation after the condensing. Impurities adhered to the surface of the sample and substances extracted at the surface of the sample can be removed by washing with the cleaner so that the surface of the sample to which these impurities and substances were adhered can be protected from such impurities, etc. being baked in the ensuing ultraviolet radiation application. Consequently, generation of spot patterns and an excessive colour change of the surface of the sample during the test can be prevented.