A holder device attaches a circular saw to a T square. The device includes a body having opposite left-hand and right-hand ends and opposite forward and rearward sides that extend between the ends. A passageway formed through the body interconnects the left-hand and right-hand ends for movably receiving the longitudinal arm of the T square. A receptacle formed in one of the sides receives the base plate of the saw to interengage the body with the saw. The lateral arm of the T square is abuttably positionable against and movable against an edge of a work piece for guiding the circular saw to make a selected cut in the work piece.