To prevent an image failure such as a vertical streak, with a simple structure and also prevent an ozone deterioration of a corona electrifier.

The image forming device has at least: an image carrier (1) which is movable; and the corona electrifier (2) which is disposed opposite to the image carrier, has an open face opposite to the image carrier and at least one ventilation opening (6), and is provided with a conductive shield (3) surrounding a wire-like discharge electrode (4). In the image forming device, the conductive shield has at least a nearest contact face (7) that is the nearest to the discharge electrode, and at least a second ventilation opening (8) is formed in a face that is not nearest to the discharge electrode.