PURPOSE: To prevent any premature outward exclusion of bottles from taking place by forcing bottles subjected to conveyer transport to pass an optical distance measuring device every time of their return, radiating light beams on the circumferential edge range on the bottle bottom parts from a measuring device and owing to the evaluation result of a distance measuring signal, bottles are separated and excluded outside of circulation process flow.

CONSTITUTION: A laser distance measuring device 5 is installed at an interval to a pet bottle 1, light point is injected on the bottle 1 along an arrow mark A and reflected light beams are condensed in an image at a position sensor inside of the device 5 by means of an objective lens 4. The sensor inputs an analog signal proportional to a measured distance into an analytic device 6. The bottle 1 makes relative movement to the device 5 by means of a conveyer and the locus of a light point exceeds the base surface 2 on the bottle 1 and extends to the outside peripheral range of a dome 3 from the inside circumferential range of the base surface 2. Two curves of a measured distance signal and a reflected light quantity signal are produced from the sensor output, and these are evaluated to detect rugged state and cracked state of the surface and any bottle 1 determined unsatisfied is removed and separated to the outside of the conveyer.