Abstract: A chain saw conversion unit for a portable power-driven circular saw is provided wherein the saw blade is replaced by a sprocket and the base plate of the saw is engaged between two adjustable attachment plate members having channel ends engaging the ends of the base plate of the saw, one of the attaching plates having a side flange below the sprocket carrying an adjustable blade bracket on which a cutter bar is attached at an angle to the plate and a saw chain is mounted around the cutter bar and sprocket. A friction clutch sprocket is provided to permit slippage in event of overload.