PURPOSE: To prevent temperature rise of a photosensitive drum, to miniaturize it, and to suppress scattering of a developer, by providing the drum with air leakage preventing means, and introducing the outer air into the drum to cool it.

CONSTITUTION: A hollow shaft 24 for supporting a photosensitive drum 22 penetrates the side plates 23a and 23b, one end of the shaft 24 is connected to a sirocco fan 32, and the other end to an exhausting pipe. The drum 22 is rotated on bearings 29a, 29b also being used for air leakage prevention. The surrounding air drawn into the drum with the fan 32 is exhausted through an air exhaust opening 27 to the outside, thus permitting temperature rise of the drum to be prevented, the apparatus to be miniaturized, and a developer and dust to be prevented from scattering.