An air cleaner which is free from a conventional disadvantage that, when an ionizing unit is removed from a body housing for cleaning, an ionizing wire is broken at an erroneous touch of it, wherein a pre-filter (7) is installed removably in front of an ionizing/dust collecting unit (ionizing unit) (6), the pre-filter (7) being slid by being guided by the guide slat (23) of a sub-frame (12) for installation in front of the sub-frame (12). An installed pre-filter (7) does not expose ionizing wires (15) to thereby protect the wires (15), whereby such a disadvantage is eliminated that ionizing wires (15) are broken while the ionizing/dust collecting unit (6) is being removed from the body housing, because there is no possibility of erroneously touching the wires (15).