PURPOSE: To detect flaws in the member and to simplify and miniaturize the device by arranging the face surface anf the back surface of the tape member in parallel, and scanning said parallel parts by using a single light emitting device and a plurality of light receiving devices.

CONSTITUTION: The copper tape 10 as an object to be measured is turned over by a roll 11 and its conveying direction is changed. The horizontal position of a feeding part X of the tape 10 to the roll 11 and an outgoing part Y are shifted so that they are not overlapped in the vertical direction. The light emitting device 12 emits a light beam 13 to the parallel face surface and back surface of the tape 10 at a specified angle. The entire areas in the width direction of both surfaces are uniformly lit. The reflected light beams 14 and 15 from the face/ back surfaces of the tape 10 are inputted to the light receiving devices 16 and 17 and converted into signals. Thus sudden change in the converted outputs is detected and the face/back surfaces are checked.