An air cleaner of the present invention includes a housing having an upper wall and side walls, a fan, a supporting plate extending between the two side walls for supporting the fan, a first air flow directional member extending between the supporting plate and the upper wall, and a second air flow directional member provided at a horizontal periphery of the housing. The first air flow directional member not only provides reinforcement to the supporting plate and the upper wall, but also directs an air flow output from the fan. The second air flow directional member has a horizontal plate and vertical plates for directing air flow at the horizontal periphery of the housing. The first air flow directional member and the second air flow directional member are adapted to equalize a velocity of an air flow distributed across an air flow output area of the fan unit. The supporting plate and the first air flow directional member are adapted to maintain a predetermined spacing between a predetermined portion of the fan and the first air flow directional member. The air cleaner of the present invention can reduce energy consumption by improving efficient of the fan.