PURPOSE: To prevent erroneous inspection by stopping a case for necessary seconds after vibrating it, and then by inspectng the internal pressure of a group of canned food packed in the case by a stroke checking machine.

CONSTITUTION: When a case 1 is put upside down and vibrated by a shaker, canned food packed with viscous contents is inverted with a lid α3, having a tab , down and air bubbles and sediment γ' sticking the internal surface of the lid α1 are washed off. When the case 1 is mounted on a still conveyor 3 while inverted, the conveyor 1 is in a still state 3W15 seconds substantially by moving with delay, so that the contents γ fall from the lid α1 completely. A group of the canned food free from deformation and the sticking of the contents, etc., is applied with electromagnetic impulses by a stroke checking machine 4 to inspect the internal pressure of the canned food group without erroneous inspection.