An air cleaner includes a base member including a base wall extending substantially horizontally, and a cover member attached to an upper side of the base wall to jointly define a filter chamber for receiving a filter element therein. The air cleaner further includes a passage member communicating with the filter chamber and incorporated with a plurality of air ejection pipes each surrounded by an annular air inlet passage fitted with guide vanes for rotating the air flow, and a case member defining separation chambers for separating dust from the rotating air flow. The passage member is interposed between the cover member and the case member.