There is provided a portable power working machine, which is capable of rationally and effectively preventing the generation of the icing without giving rise to early clogging of air cleaner, the malfunction of a internal combustion engine and deterioration of performance. This working machine comprises a small air-cooled internal combustion engine which is mounted inside a main housing, a cooling fan disposed on one side of the main housing; a carburetor coupled to an upper portion of an intake port of the internal combustion engine; a clean air chamber disposed on an upstream side of the carburetor; an air cleaner cover coupled to the clean air chamber; a warm air introducing passageway for introducing, through a region adjacent to the intake port, part of air which has been sucked by the cooling fan for cooling the internal combustion engine into the air cleaner cover; and a shutter for and externally opening or closing the warm air introducing passageway as desired.