PURPOSE: To make it possible to output a stable image in the case temperature and humidity changes by varying the intensity of exposure by the use of an exposure intensity control means based on temperature and humidity and also providing a developer temperature control circuit which keeps the temperature of developer constant.

CONSTITUTION: The device is provided with a liquid temperature sensor 25 which detects the temperature of developer; an exposure scanner 15 which controls the exposure intensity of a laser exposure means according to at least temperature or humidity of the ambient atmosphere of a drum 10 detected by a temperature sensor 28 and a humidity sensor 29; and the developer temperature control circuit 30 which exerts control according to the temperature of the developer, detected by the liquid temperature sensor 25, so that the developer is maintained at the prescribed temperature. The exposure scanner 15 corrects the value of the exposure intensity according to environmental data transferred from the temperature and humidity sensors 28 and 29, respectively, and the laser exposure means carries out exposure according to the corrected intensity of exposure. The developer temperature control circuit 30 detects the temperature of the developer by means of the liquid temperature sensor 25 and exerts control so that the developer is maintained at the preset temperature.