An embodiment of the present invention relates to a deep freezer. A deep freezer according to an embodiment of the present invention comprises a plurality of heat exchangers installed to an inlet pipe and performing a heat exchange of a mixed refrigerant suctioned into a compressor. The mixed refrigerant comprises: a high temperature refrigerant which is one selected from among butane (N-butane), 1-butene, and isobutane; and a low temperature refrigerant consisting of ethylene.