To enhance heat insulation effect of a freezing chamber which is kept at extremely low temperature by a dual refrigerator.

A vertical extremely low temperature freezer 1 comprises a heat insulating box member 7 formed in a composite structure constituted of a vacuum heat insulating panel 5 and a foamed heat insulating material 6, a heat insulating door 8 formed in a composite structure constituted of the heat insulating panel 5 and the foamed heat insulating material 6 and a dual refrigerator 14 for cooling an article contained in the interior of the heat insulating box member 7. The dual refrigerator 14 is formed by cascade connection of a high temperature side refrigerant circuit and a low temperature side refrigerant circuit to generate extremely temperature.