PURPOSE: To detect a defect with stable accuracy by rotating an object of inspection, rotating a member which differs in reflection factor from the object in elastic contact, and detecting the difference in the quantity of reflected light of a contacting part.

CONSTITUTION: The discoid object 1 to be inspected which has a projection step part 2 is placed on a rotary disk and the object part 3 of inspection is inspected. When the object part 3 is, for example, black and has a low reflection factor, the white reflecting member 4 which has a high reflection factor and is made of 'Teflon(R)', etc., is brought into contact with the object part 3 elastically. Then, the reflecting member 4 is rotted together with the object 1. The area A of the contacting part between the object part 3 and member 4 is measured by a reflected light quantity gauge to measure the entire surface of the object part 3 every time the object body 1 makes one turn. The surface defect of the object part 3 is detected from the difference in the quantity of reflected light between the both. For the purpose, members which differ in reflection factor are rotated in contact with the outer peripheral edge 7 of the object part and the difference in the quantity of reflected light is measured, so the defect is detect with high accuracy.