A second duct 50 for guiding air outside an image forming apparatus A to a charging device 2 includes: a first flow passage 50c; a second flow passage 50d bent from the first flow passage 50c and extending in a direction orthogonal to a rotational direction and a rotational axis direction of a photosensitive drum, the second flow passage 50d being provided with an outlet 50b; and a plurality of flow dividing plates 60 provided in the second flow passage 50d, the plurality of flow dividing plates 60 being disposed in parallel along the rotational axis direction and forming a third flow passage between the flow dividing plates 60 adjacent to each other, in which a relationship between a length in the orthogonal direction and a length in the rotational axis direction of the third flow passage is a predetermined relationship.