To provide a guide roller wearing detector device for a wire saw whereby wearing of a guide roller can be surely detected.

When a groove 16A of a guide roller 16 is worn by a prescribed amount, a detection bar buried in the guide roller 16 is exposed in the groove 16A. The detection bars exposed in the groove 16A are connected to each other through a wire, as a result, a current flows in a circuit, a light emitting diode 82 emits light. By receiving light emitted from this light emitting diode 82 through a light receiving sensor 84, the guide roller 16 is detected to be worn by the prescribed amount.