Abstract: An optical device comprising an illuminator, a receiver located below the illuminator and a scanner. The scanner is designed as two identical mirror prisms rigidly coupled to each other and rotatably mounted on a common axle. One of the prisms intercepts the light beams of the illuminator. The other prism is placed below the former so that it intercepts the light beams reflected from the light-contrast pattern bearing surface being explored and directed to the receiver. A gap is provided between the mirror prisms which accommodates a partition made of a light-tight material. The casing is provided with two viewing windows which correspond to said mirror prisms. The above design of the scanner makes it possible to use the optical device in automatic guidance systems on board vehicles operating under any environmental conditions both in the day-time and at night on various surfaces bearing a light-contrast pattern.