A turbo-Brayton refrigeration machine (11) includes a first circulation path (L1) in which a first refrigerant circulates, a second circulation path (L2) in which a second refrigerant which is a cooling target circulates, a subcooler (22) disposed over the first circulation path (L1) and the second circulation path (L2) and configured to have a single heat-exchanging unit, and an expansion turbine (21) positioned on a primary side of the subcooler (22) in the first circulation path (L1), in which the pressure ratio of the expansion turbine (21) is the pressure ratio at which the outlet temperature of the expansion turbine (21) is higher than a freezing point of the second refrigerant.