PURPOSE: To quicken switching of machine and response to occurrence of defective product by detecting the switching indication of preceeding jig on a conveyor through assembling machine in respective processes while detecting defective jig indication through the assembling machine in next process.

CONSTITUTION: The final assembling jig 1 is detected through a terminal counter to push out only one informing pin 10 through switching unit to be detected by a switching detector 21b of jig stacker at the starting end of conveyor 5. Then it is detected by the detector 21b of assembling machine in respective processes and fed to push in the informing pin 10 through the terminal switching unit then decided to be an old jig by the indication at the machine type specifying section 13 and collected. Consequently, the jig stacker and the assembling machine will correspond quickly to next machine type thus to start assembling. At the time point when it is decided to be defective by a recognizing unit in the way of assembling machine, the defective information pin 14 is pushed out and detected through a detector 21c of assembling machine in the next process to be removed quickly.