Abstract: In case of detecting tire information marks engraved in a side wall portion of tire in the form of protrusion or recess, width and inner diameter of tire are detected to provide a tire size signal, after a first camera head is driven into a given position in accordance with the tire side signal, an identification mark engraved in the size wall portion of tire is optically detected by the first camera head to derive a position signal, and after a second camera head is driven into a given position in accordance with the position signal, the tire information marks are optically detected by the second camera head to derive a tire information signal. In this manner, the tire information marks can be detected in a rapid and accurate manner.

Abstract: Tire information marks for denoting tire kind, tire size, etc. formed in a surface of side wall of tire as protrusion or groove having a triangular cross section are optically detected by illuminating the surface of side wall of tire from a first direction substantially perpendicular to the surface of side wall of tire and a second direction inclined with respect to the surface of side wall of tire, and picking up an image of the surface of side wall of tire thus illuminated from the two different directions to derive an image signal. The image signal thus derived is converted into a bivalent signal, and is thinned to produce a mark pattern. Then the mark pattern is compared with a thick standard mark pattern. When a substantial part of the detected mark pattern is included in the standard mark pattern, the detected mark pattern is recognized to be identical with the standard mark pattern.