PURPOSE: To decompose and dissipate ozone by making the ozone retained in a machine by providing a guiding member which regulates the sending direction of discharged air by an air blower for cooling the inside of the machine and making the ozone leaked from a gap communicating the inside to the outside of the device retained in the machine.

CONSTITUTION: A housing 40 constituting an optical system cooling fan 29 is provided with U-shaped ducts 31 and 32 at both ends of a fan, and a motor 33 is arranged in the duct 32. The air blower means for sending cooling air to a heat generating member by sucking outside air is formed of the fan 29, the U-shaped ducts 31, 32 functioning as the guiding member for the discharged air of the fan 29 in the air sending direction, and the housing 40. The air flow F4' including the ozone from the conventional ozone generating source (electrostatic chargers 3, 6 and 7) is not generated by the divided flows F2, F3 of the U-shaped ducts 31, 32, and becomes retaining flow F4 as shown in Figure. Thus, the air with high ozone concentration mechanically is retained, and the ozone is not rapidly discharged to the outside of the machine as in the conventional device, and the ozone is removed due to the natural dissipation of the ozone while it remains in the machine and the decomposition of the ozone by a temperature in the machine.