A belt inspecting apparatus applies illuminating light beams (R, G, B) through light guides to a flat inner portion, a flat outer portion, flat side portions, and curved portions of a metal belt. The illuminating light beams, which are reflected by the metal belt, are guided through the light guides to color cameras, which detect the illuminating light beams as image information. A surface state decision unit compares the detected image information with normal image information in order to determine whether the metal belt contains flaws therein or not.