An image forming apparatus includes a main body of the image forming apparatus; a developing cartridge that is detachably disposed in the main body and includes an image carrier; a charging roller that is disposed to face the image carrier in the developing cartridge and charges a surface of the image carrier; a charging roller separating unit that moves the charging roller between a first position in which the charging roller is in contact with the image carrier and a second position in which the charging roller is spaced apart from the image carrier; and a paper feeding cassette detachably disposed in the main body; wherein when the paper feeding cassette is first mounted, the charging roller is fixed in the second position by the charging roller separating unit.