AIR CLEANER

Provided is an air cleaner including: a first case and a second case each having a case wall; and a flat plate filter element sandwiched between the first case and the second case, wherein the flat plate filter element has an annular sealing portion on a peripheral edge of the flat plate filter element, at least a partial section of a peripheral edge of at least one of the first case or the second case has a flange portion and a guide wall inside the case wall, the flange portion contacts the sealing portion and extends inside at least one of the first case or the second case substantially perpendicular to the case wall from an end of the case wall, and the guide wall extends substantially parallel to the case wall and facing the case wall from an inner end of the flange portion.