A temperature and humidity compensating device is provided in electrophotographic apparatus including a photosensitive medium having a photoconductive layer, an image forming unit for forming an electrostatic latent image on the photosensitive medium, a heat source disposed near the photosensitive medium for heating the latter, a temperature detector disposed remotely from the heat source for detecting the temperature of the photosensitive medium, and control means for controlling the heating of the heat source so that the temperature of the photosensitive medium detected by the detector is not lower than the ambient temperature. Thus, the photosensitive medium may be prevented from deterioration due to falling temperature and moisture absorption, thereby permitting a normal image formation to be achieved.