PURPOSE: To enhance the accuracy of the detection of such defect as chip of an article such as a pellet during the intermittent conveyance of a continuous film with which the article is wrapped, by detecting a mark on a rotary disk on the output shaft of a feed driver to find out the conveyed position of the film.

CONSTITUTION: When a feed driver 2 is in operation, a slider 24 is reciprocated on a parallel guide shaft 25 through a link 29 and a lever 28 by one rotation of a cam 32 on a main cam shaft 11 so that a wrapping film 1 is intermittently conveyed. At that time, a signal of frequency and pulse width corresponding to the conveyance speed of the film 1 is sent from a rotary encoder 9 to an electronic circuit 100. A timing signal, which corresponds to the time when the tip of each of seats SH1WSH5 corresponding to desired conveyed positions has arrived right under a solid camera 4, is also sent to the electronic circuit 100 from a photocoupler 13 facing a slitted disk 12 on the main cam shaft 11. The electronic circuit 100 can detect a chip on the basis of the output signal of the solid camera 4.