An image forming apparatus is provided with a casing, a drum unit including a photoconductive drum having a central axis extending in a first direction, and a charging device configured to charge the photoconductive drum, a fixing unit configured to fix an image on a printing medium, a fan configured to generate an air flow inside the casing, a filter configured to remove ozone included in the air, a first channel defined in the casing, the air directed from the fixing unit toward the fan flowing in the first channel, a second channel defined in the casing, the air directed from the charging device toward the fan flowing in the second channel, the filter being provided in the second channel, the second channel being arranged next to the first channel, and a blocking member configured to block communication between the first channel and the second channel.