PURPOSE: To easily and securely cut off a side zipper part with its strength secured by forming half-punched perforations which pass only through a rear sheet and a corrugated sheet but not through a surface sheet on the side zipper part.

CONSTITUTION: A side zipper part 20 provided at a position for cutting a body of an individual case A laterally is formed with half-punched perforations 24 which pass only through a rear sheet 25 and a corrugated sheet 26 but not through a surface sheet on upper rim and lower rim positions of the side zipper part. When individual cases A with the side zipper parts unopened are to be stacked, strength of the zipper parts is secured, so that the cases may not bend nor be crushed. When the side zipper part 20 is to be unsealed, a finger is put from a cutting end of the zipper part to cut one of the zipper parts open, whereby the surface sheet 27 can easily be broken by utilizing the half-punched perforations for cutting the zipper part 20 off and making a tray for product display.