NOVELTY - A freezer unit comprises nonazeotropic mixed refrigerants containing (i) R245fa, R600, R404A, R508A, R14, R50, and R740, (ii) R245fa, R600, R404A, R23, R14, R50, and R740, or (iii) R245fa, R600, R404A, R508B, R14, R50, and R740 confined in the refrigerant circuit on the low temperature side.    USE - For a two-dimensional refrigeration system.    ADVANTAGE - The invention provides a freezer unit using refrigerants serving as an oil carrier and being capable of realizing extremely low temperatures, e.g. -150degreesC, without using any refrigerants which are subjects of the ozone regulation.    DETAILED DESCRIPTION - A freezer unit comprises a refrigerant circuit (2) on a high temperature side and a refrigerant circuit (3) on a low temperature side to form independent closed refrigerant circuits which condense refrigerants delivered from compressors (4, 10) and evaporate the condensed refrigerants to achieve cooling action; and heat exchangers formed by an evaporator (14) in the refrigerant circuit on the high temperature side and a condenser (8) in the refrigerant circuit on the low temperature side. Nonazeotropic mixed refrigerants containing (i) R245fa, R600, R404A, R508A, R14, R50, and R740, (ii) R245fa, R600, R404A, R23, R14, R50, and R740, or (iii) R245fa, R600, R404A, R508B, R14, R50, and R740 are confined in the refrigerant circuit on the low temperature side.    DESCRIPTION OF DRAWING(S) - The figure shows refrigerant circuits of the freezer unit.    Refrigerant circuit (2, 3)    Compressors (4, 10)    Delivery pipe (4D, 10D)    Suction pipe (4S, 10S)    Auxiliary condenser (5)    Dew preventing pipe (6)    Oil cooler (7)    Condenser (8)    Condenser blower (9)    Dryer (12, 28, 35, 39, 45)    Pressure-reducing device (13, 36, 40, 46, 52)    Evaporator (14)    Accumulator (15)    Oil separator (18)    Oil-restoring pipe (19)    Condensation pipe (23)    Cascade condenser (25)    Gas-liquid separator (29, 33)    Gas phase pipe (30, 43)    Intermediate heat exchanger (32, 42, 44)    Gas-liquid separator (33)    Liquid phase pipe (34, 38)    Evaporating pipe (47)    Expansion tank (51)