Radiation tolerance of a field emitter array and a cadmium telluride-based photoconductor was investigated. The variation of the performance of these devices were investigated during the gamma-ray irradiation by every 100 - 200 kGy. Total dose of irradiation reached 1.2 MGy, but no significant deterioration of the properties has been observed. A test tube exhibited successful photo-signal detection even after the irradiation of 1 MGy. As a result, it was found that the field emitter array and the photoconductor have sufficient radiation tolerance against gamma-ray irradiation.