PURPOSE: To prevent the passage of a defective can when mingled on the side of discharging acceptable cans owing to a mechanical disorder, by detecting that the defective can is carried to the discharge side.

CONSTITUTION: When a can 3 is carried to an unloading position 7, failing to be discharged as a defective can at a defective can discharge port 12 while a light leak is detected from the can 3 at a testing position, it is detected with a can presence sensor 15 and a defective can existence signal is sent to an interface from a defective can existence signal generation circuit. The interface starts a solenoid valve for preventing the passage of defective cans through a main motor interlock or the like to stop the rotation of a turret disc 1 and an alarm is outputted while the flow of the can 3 is halted. In other words, a tester is stopped and simultaneously with the outputting of an alarm, the solenoid valve for preventing the passage of defective cans is operated to supply air to an air nozzle 16 thereby enabling prevention of the passage of defective cans.