PURPOSE: To accurately observe the object to be observed with sufficient contrast ratio, by locating a light source illuminating the object almost vertically via an optical diffusing member, and locating the means observing the object at a location where reflected light can be incident from the object by this light source.

CONSTITUTION: The device observing the object 2 to be observed having higher reflection factor with lustre such as polyvinylchloride and aluminum foil, is provided with illuminating light sources 3a, 3b almost vertically illuminating the object 2 via optical diffusion members 10a, 10b and 10c, 10d. Further, at a location where the reflected light from the object 2 by the light sources 3a, 3b can be incident, a pickup camera 4 observing the object 2 via a shield cylinder 11 is located, and the camera 4 is connected to a processing circuit 5. Further, the contrast of image incident to the camera 4 is sufficiently taken to make accurate the observation of the object 2 moved with a belt conveyor 1.