A fastener driving device includes a frame structure providing a handle portion and an adjustable annular exhaust air directing member mounted on the frame structure. The exhaust air directing member allows air displaced during the operation of the device to be directed by a rotational position thereof. A pair of O-rings are provided which act between the exhaust air directing member and the frame structure (1) to ensure that air is discharged into the atmosphere in a direction determined by the rotational position of the exhaust air directing member and (2) to yieldingly retain the exhaust air directing member in any rotational position into which it is manually moved. The frame structure includes a cylinder housing portion integral with the handle portion. A cap member is bolted in sealing relation to the cylinder housing portion and the exhaust air directing member is rotatably mounted to the cap member.