A laser light beam guiding device on a stone cutter includes a tubular main body pivoted to a lug of a seat which is secured to a front top of a blade guard of the stone cutter, a battery chamber in the main body controlled by a switch button on the top, a tubular sleeve on the rear portion of the main body and a laser projector rotatably engaged with the front end of the main body to emit the light beam on a working piece to decide a cutting line for the saw blade to follow up.