PURPOSE: To deeply freeze the air in a container and to maintain it at a cryogenic temperature by mounting freezing units at both ends of a rectangular parallelepiped container and providing a door at least one sidewall of the container.

CONSTITUTION: When freezing units 100 are operated, the air in a deep freezing container is sucked into evaporation sections 15 of the units 100, cooled through an evaporator 10, and then introduced into ventilating rails 43 through a diffusing chamber 18. Most of the air is diffused from gaps of the rails 43 into the container 1, but part is guided to an air guide 44, directed upward, and diffused into the container 1. A cargo is discharged from and introduced into the container by opening a door 45. Thus, the air temperature in the container can be maintained at -55--35°C.