PURPOSE: To check the number of sheets in a quick and assured way, by retrieving whether the most outer projection part on the blister face of each sheet is at a prescribed position by means of the retrieving tools of a number corresponding to a prescribed number of sheets.

CONSTITUTION: The levers 61 serving as retrieving tools are provided to the supports 63 and 63 by 5 pieces each for example and centering on a spacer 62 so that they are set at both sides in the shifting direction of each stage of an object to be checked. Thus the number of stacked blister pack sheets 1. The lever 61 is energized by a spring 64 to be put more inside than the position of the most outer projection part 12A on the blister face of the sheet 1. Furthermore a stopper 65 is provided to prevent the lever 61 from having displacement larger than a prescribed level. Then the detecting part 61A of the lever 61 receives a normal displacement to the outer side by the part 12A in the retrieving mode and owing to a relative shift of an object to be checked and the detecting part of a defective product. When all lever 61 have displacement, the plunger of a microswitch 66 is opened. The plunger has no displacement if the part 12A has a crack.