PURPOSE: To cause a slight cut made only lengthwise along the middle of film to accurately proceed while tearing the film across its width under a light force by fixing a means for making a small cut in film to the central end part of the rear surface of a covering piece and providing a weakening line extending from the nearly central end part of the covering piece to both the ends thereof.

CONSTITUTION: A rectangular case having a front plate 1, a bottom plate 2 and a rear plate 3 made up successively and continuously with ridge lines formed therebetween and nearly square side plates 4 secured to both the ends thereof is made, a lid 5 is formed extending from the upper edge of the rear plate 3 of the case and a covering piece 6 is provided extending from the side edge of the lid 5 to overlap the front plate 1. A means for making a slight cut in a film 9 is fixed to the central end part of the rear surface of the covering piece 6 or the center of the outer surface of the front plate 1 to be placed into contact with the end part of the covering piece 6 and the covering piece 6 is provided with a weakening line 10 extending from its nearly central end part to both the ends thereof, whereby the deformation of the end part of the covering piece 6 is increased under tension by the film 9.