The purpose of this study was to examine the possibility of early diagnosis on plants' abnormal symptoms caused by blight from Cladosporium cucumerium and Colletotrichum orbiculare which are often found in cucumbers before they are observed with the naked eye through nondestructive and contactless analysis using an infrared thermography camera. According to the results, concerning Cladosporium cucumerium, 5 th day after pathogenic fungus inoculation, the region inoculated tended to indicate lower temperature than other regions not inoculated. 9 th day after the inoculation, the symptoms were observed with the naked eye. About Colletotrichum orbiculare, seven days after the inoculation, temperature in the region inoculated was getting lower, and 13 th day after the inoculation, the symptoms were observed with the naked eye. Therefore, infrared thermography camera can be used to conduct early diagnosis before plants' abnormal symptoms caused by blight are seen with the naked eye.