A refrigeration apparatus (10A, 10B, 10C, 10D) including: a cooling device which is configured to be disposed in a freezer (30a, 30b), and includes a casing (34a, 34b), a heat exchanger pipe (42a, 42b) with a difference in elevation disposed in the casing, and a drain receiver unit disposed below the heat exchanger pipe (42a, 42b); a refrigerating device configured to cool and liquefy CO 2 refrigerant; a refrigerant circuit (12, 14) for permitting the CO 2 refrigerant cooled and liquefied in the refrigerating device to circulate to the heat exchanger pipe (42a, 42b), and a defrost system, the defrost system comprising: a bypass pipe (52a, 52b) connected between an inlet path and an outlet path of the heat exchanger pipe (42a, 42b) to form a CO 2 circulation path including the heat exchanger pipe (42a, 42b); a bypass valve (53a, 53b) disposed in the bypass pipe (52a, 52b) and configured to be opened at a time of defrosting, an on-off valve (54a, 54b) disposed in each of the inlet path and the outlet path of the heat exchanger pipe and configured to be-closed at a time of defrosting so that the CO 2 circulation path becomes a closed circuit; a pressure adjusting unit (45a, 45b) for adjusting pressure of the CO 2 refrigerant circulating in the closed circuit at the time of defrosting; and a brine circuit in which brine as a first heating medium circulates and which includes a first lead path (63a, 63b) disposed adjacent to the heat exchanger pipe (42a, 42b) in the cooling device and forming a first heat exchanger part for heating the CO 2 refrigerant circulating in the heat exchanger pipe (42a, 42b), with the brine, in a lower area of the heat exchanger pipe, wherein the defrost system configured to permit the CO 2 refrigerant to naturally circulate in the closed circuit at the time of defrosting by a thermosiphon effect. a cooling device which is configured to be disposed in a freezer (30a, 30b), and includes a casing (34a, 34b), a heat exchanger pipe (42a, 42b) with a difference in elevation disposed in the casing, and a drain receiver unit disposed below the heat exchanger pipe (42a, 42b); a refrigerating device configured to cool and liquefy CO 2 refrigerant; a refrigerant circuit (12, 14) for permitting the CO 2 refrigerant cooled and liquefied in the refrigerating device to circulate to the heat exchanger pipe (42a, 42b), and a defrost system, the defrost system comprising: a bypass pipe (52a, 52b) connected between an inlet path and an outlet path of the heat exchanger pipe (42a, 42b) to form a CO 2 circulation path including the heat exchanger pipe (42a, 42b); a bypass valve (53a, 53b) disposed in the bypass pipe (52a, 52b) and configured to be opened at a time of defrosting, an on-off valve (54a, 54b) disposed in each of the inlet path and the outlet path of the heat exchanger pipe and configured to be-closed at a time of defrosting so that the CO 2 circulation path becomes a closed circuit; a pressure adjusting unit (45a, 45b) for adjusting pressure of the CO 2 refrigerant circulating in the closed circuit at the time of defrosting; and a brine circuit in which brine as a first heating medium circulates and which includes a first lead path (63a, 63b) disposed adjacent to the heat exchanger pipe (42a, 42b) in the cooling device and forming a first heat exchanger part for heating the CO 2 refrigerant circulating in the heat exchanger pipe (42a, 42b), with the brine, in a lower area of the heat exchanger pipe, wherein the defrost system configured to permit the CO 2 refrigerant to naturally circulate in the closed circuit at the time of defrosting by a thermosiphon effect. a bypass pipe (52a, 52b) connected between an inlet path and an outlet path of the heat exchanger pipe (42a, 42b) to form a CO 2 circulation path including the heat exchanger pipe (42a, 42b); a bypass valve (53a, 53b) disposed in the bypass pipe (52a, 52b) and configured to be opened at a time of defrosting, an on-off valve (54a, 54b) disposed in each of the inlet path and the outlet path of the heat exchanger pipe and configured to be-closed at a time of defrosting so that the CO 2 circulation path becomes a closed circuit; a pressure adjusting unit (45a, 45b) for adjusting pressure of the CO 2 refrigerant circulating in the closed circuit at the time of defrosting; and a brine circuit in which brine as a first heating medium circulates and which includes a first lead path (63a, 63b) disposed adjacent to the heat exchanger pipe (42a, 42b) in the cooling device and forming a first heat exchanger part for heating the CO 2 refrigerant circulating in the heat exchanger pipe (42a, 42b), with the brine, in a lower area of the heat exchanger pipe, wherein the defrost system configured to permit the CO 2 refrigerant to naturally circulate in the closed circuit at the time of defrosting by a thermosiphon effect.