A refrigeration system comprising: a heat converter for condensation that changes high-temperature and high-pressure refrigerant gas discharged from a compressor of a refrigeration system to low-temperature refrigerant liquid, comprising: an isobaric cooling unit adapted to cool the high-temperature and high-pressure refrigerant gas under isobaric change; a pressure-reducing and liquefying unit adapted to liquefy the refrigerant gas a part of which is liquefied in the isobaric cooling unit by reducing the pressure and the enthalpy of the refrigerant by an acceleration phenomenon of the refrigerant; and a pressure-reducing and cooling unit adapted to cool the refrigerant passed through the pressure-reducing and liquefying unit by further reducing the pressure and the enthalpy of the refrigerant along a saturated liquid line by the acceleration phenomenon of the refrigerant, an evaporator adapted to suck low-temperature refrigerant liquid from the heat converter for condensation and to heat-exchange the low-temperature refrigerant liquid with a cooling target to cool the cooling target; a compressor that is connected to the evaporator through a suction pipe and adapted to compress refrigerant which is partially or wholly vaporized in the evaporator; and a refrigerant pipe (2, 4, 10) through which the compressor and the heat converter for condensation are connected to each other and the heat converter for condensation and the evaporator are connected to each other, characterized in that respective flow passages of the isobaric cooling unit, the pressure-reducing and liquefying unit, and the pressure-reducing and cooling unit are designed to be narrower in this order, the isobaric cooling unit is a mini heat exchanger adapted to liquefy 5 to 50 wt% of the high-temperature and high-pressure refrigerant gas discharged from the compressor and the cross-sectional area of the flow passage of the pressure-reducing and liquefying unit is set to 40 to 50% and the cross-sectional area of the flow passage of the pressure-reducing and cooling unit is set to 20 to 30% with respect to the cross-sectional area of the flow passage of the isobaric cooling unit. an isobaric cooling unit adapted to cool the high-temperature and high-pressure refrigerant gas under isobaric change; a pressure-reducing and liquefying unit adapted to liquefy the refrigerant gas a part of which is liquefied in the isobaric cooling unit by reducing the pressure and the enthalpy of the refrigerant by an acceleration phenomenon of the refrigerant; and a pressure-reducing and cooling unit adapted to cool the refrigerant passed through the pressure-reducing and liquefying unit by further reducing the pressure and the enthalpy of the refrigerant along a saturated liquid line by the acceleration phenomenon of the refrigerant, an evaporator adapted to suck low-temperature refrigerant liquid from the heat converter for condensation and to heat-exchange the low-temperature refrigerant liquid with a cooling target to cool the cooling target; a compressor that is connected to the evaporator through a suction pipe and adapted to compress refrigerant which is partially or wholly vaporized in the evaporator; and a refrigerant pipe (2, 4, 10) through which the compressor and the heat converter for condensation are connected to each other and the heat converter for condensation and the evaporator are connected to each other, characterized in that respective flow passages of the isobaric cooling unit, the pressure-reducing and liquefying unit, and the pressure-reducing and cooling unit are designed to be narrower in this order, the isobaric cooling unit is a mini heat exchanger adapted to liquefy 5 to 50 wt% of the high-temperature and high-pressure refrigerant gas discharged from the compressor and the cross-sectional area of the flow passage of the pressure-reducing and liquefying unit is set to 40 to 50% and the cross-sectional area of the flow passage of the pressure-reducing and cooling unit is set to 20 to 30% with respect to the cross-sectional area of the flow passage of the isobaric cooling unit.