The present invention relates to an improvement of a charging unit of an electrophotographic image forming apparatus, having a swingably openable clamshell. 
Laser beam printers are known in which, an electrostatic latent image is formed by scanning and exposing a uniformly charged photoconductive material arranged on a photoconductive drum by a laser beam modulated in accordance with image data, such as figures, characters and the like, in order to obtain a hard copy of the image data through an electrophotographic image forming process, comprising the steps of developing, transferring, and fixing. 
In a laser beam printer, an electrostatic photoconductive material is provided on the circumferential surface of a photoconductive drum.  Around the photoconductive drum, a charging unit, exposing unit, developing unit, transferring unit, cleaner unit, and discharging unit are disposed, as viewed in the direction of rotation of the photoconductive drum. 
The photoconductive material on the surface of the photoconductive drum, which is uniformly charged by the charging unit, is exposed by a laser beam carrying image data, at the exposing unit, in order to form a latent image on the photoconductive material.  Toner is then stuck to the latent image by the developing unit for development (forming a toner image), and the toner image is transferred onto a recording sheet, which is fed at the same speed as the peripheral speed of the photoconductive drum at the transferring unit.  The toner image transferred onto the recording paper is then heated or pressed by the fixing unit, and, thus, the toner image is fixed onto the recording sheet.  Then the recording sheet, carrying the fixed image thereon, is ejected from the printer. 
Generally, the transferring unit is disposed below the photoconductive drum, and the charging unit and a scanning optical system, forming the exposing unit, are disposed above the photoconductive drum. 
The photoconductive drum must be replaced at a predetermined operation time, depending on the life of the photoconductive material thereof.  Generally, the photoconductive drum is integrally arranged as a drum unit with the cleaner, charging unit (i.e., the corona charger) and the like having a predetermined positional relationship with respect to the photoconductive drum. 
Further, in the laser beam printer as described above, a clamshell is arranged to be swingably opened to carry out maintenance, and to load a recording sheet when a continuous recording sheet is used. 
The charging unit is provided with a corona charge comprising a thin metal wire of tungsten or the like interposed between oppositely disposed electrode plates extending in the axial direction of the photoconductive drum, and the photoconductive material provided on the photoconductive drum is uniformly charged with the corona charger. 
When the corona charger discharges, ozone is produced, and the ozone should be allowed to escape therefrom.  One method for causing the ozone to escape from the corona charger is a method in which the upper side of the corona charger is opened in order to enable ozone produced by the corona charger to escape therefrom. 
When the clamshell is swingably opened, a problem arises in that, because the upper portion of the corona charger of the charging unit should be opened, the photoconductive drum is exposed to ambient light through the opening which is formed on the upper side of the corona charger.  Since the photoconductive material on the surface of the photoconductive drum is deteriorated by being exposed to light, the life of the drum is shortened.