To obtain a guide roller of a wire saw which can prevent splashing of a slurry.

The outer periphery of a guide roller 18 is covered with a cover 70 formed cylindrically. A wire is guided along the circumference of the guide roller 18, so that the slurry adhered to the wire splashes circumferentially. However, the outer periphery of the guide roller 18 is covered with the cover 70, so the slurry is prevented from splashing to the circumference.