To prevent water generated by cooling the steam from condensed on a surface of a packaging film without irregularities in a finished condition by implementing the heat shrinkage of the packaging film in a heated atmosphere of the steam or humidified air with the hot air.

The heat taken in an air heating chamber 8 is heated by an electric heater 9, the steam, etc., generated outside a device is ejected from spray hole 11s, a blowing fan 10 is operated, and the hot air in a wet condition in which the steam, etc., is mixed with the hot air is blown into a heat shrinkage chamber 1 from spray holes 4 in an inner wall surface 3 via a cavity 2. When a work 13 with a heat shrinkable packaging film 14 slightly covered thereon is loaded on a conveyor belt 7 and fed into the heat shrinkage chamber 1 in this heated atmosphere, the packaging film 14 is heated from its periphery with the hot air in the wet condition to implement the uniform heat shrinkage of the film without irregularities, and the film is closely stuck on a surface of the work 13 while the packaging film passes through the heat shrinkage chamber.