PURPOSE: To reduce generation of curls due to age by a method wherein after a blister package is cooled by blowing cool air to it or winding a cooling roll on it, etc., it is curved in a direction opposite to a curl of the blister package.

CONSTITUTION: A thermoplastic resin sheet 1 is wound around a feed reel 2. A blister package 1B is fabricated by heat-sealing a seal box 15 on the side of an opening of a sheet 1. The blister package 2B passes between two cones 26 of a cooling means 21 while cool air is blown to both faces of the blister package 1B. The cooled blister package 1b is sent to a curving means 22. At this curving means 22, the package 1B is curved in a direction opposite to a curl of the package 1B by making the package 1B pass through interposed between a rotary driving drum 28 and a roller 31.