Disclosed is a laser guidance system for diamond wire stone cutting apparatus. The laser guidance system includes a targeting laser light source that is fitted to one of two wire guide wheels between which the cutting wire extends and travels. A photo sensor with laser beam detectors is attached to the other wire guide wheel. During ideal operation of the cutting apparatus, the laser beam shines through the kerf in the stone being cut. When the kerf is linearly straight, as intended, the laser beam will be clearly detected by the laser beam detectors. When the kerf is not straight, the laser beam will be at least partially obscured across the cutting span, and the laser beam detectors will detect the lack of full intensity and report this to a controller so as to indicate that adjustments are necessary to re-straighten the kerf.