To provide a detector which can accurately detect a foreign matter on the bottom of a bottle by making light incident on the bottom thereof from the entire circumference of the bottle moving while being supported.

An apparatus for detecting a foreign matter on the bottom of a glass bottle 1 filled with a liquid comprises a star wheel 2 to move the bottle 1 supplied being supported by a recess part on the circumference, a ring- shaped optical fiber 10 to make light incident on the bottom of the bottle from the entire circumference of the bottle 1, a CCD camera 16 which is arranged in the course of the movement thereof 1 to image the bottom of the bottle and a light source 18 arranged at a position where light is incident into the optical fiber 10 during the imaging. The ring-shaped optical fiber 10 is connected to the star wheel 2 so that it is movable vertically concentric on the recess part of the star wheel. The ring-shaped optical fiber 10 rises above the lower end of the bottle 1 at the position of the CCD camera 16 and lowers below the lower end of the bottle 1 at the position before and after the CCD camera 16.