PURPOSE: To detect whether or not a protective cap is put over an ejection port of a container.

CONSTITUTION: A conductive conveyer 11 for transferring a conductive container 10, a non-conductive copying rod 13 which rotates in contact with the container to bypass an ejection port 12 of the container being carried by the conveyer, a conductive detecting rod 15 rotating integrally with the copying rod to touch only a non-conductive protective cap 14 put over the ejection port of the container and a detector 16 for detecting whether power is supplied between the conveyer and the detecting rod are provided. The detector 16 detects power supply if no protective cap exists.