A multistage bath condenser-reboiler , comprising: condensation passages which communicate in the vertical direction and through which a gas flows and condenses, evaporation passages which are partitioned into multiple stages which are stacked on top of each other through which a liquid flows that undergoes heat exchange with the gas and evaporates, one or more stages of liquid reservoir sections which hold liquid supplied to and discharged from the evaporation passages , and one or more liquid communication passages through which the liquid in the liquid reservoir sections flows from liquid reservoir sections to liquid reservoir sections located further downstream in the gas flow direction of the condensation passages , wherein the multistage bath condenser-reboiler comprises: a heat exchanger core comprising (i) a heat exchange section formed by adjacently stacking the condensation passages and the evaporation passages formed from plates and fins standing next to each other, and (ii) a liquid communication section formed from the liquid communication passages which are formed from plates and fins and provided on at least one side surface in a stacking direction of the condensation passages and the evaporation passages , and one or more stages of the liquid reservoir section formed on at least one side surface of the heat exchanger core perpendicular to the stacking direction of the condensation passages and the evaporation passages so as to correspond with a number of stages of the evaporation passages . condensation passages which communicate in the vertical direction and through which a gas flows and condenses, evaporation passages which are partitioned into multiple stages which are stacked on top of each other through which a liquid flows that undergoes heat exchange with the gas and evaporates, one or more stages of liquid reservoir sections which hold liquid supplied to and discharged from the evaporation passages , and one or more liquid communication passages through which the liquid in the liquid reservoir sections flows from liquid reservoir sections to liquid reservoir sections located further downstream in the gas flow direction of the condensation passages , wherein the multistage bath condenser-reboiler comprises: a heat exchanger core comprising (i) a heat exchange section formed by adjacently stacking the condensation passages and the evaporation passages formed from plates and fins standing next to each other, and (ii) a liquid communication section formed from the liquid communication passages which are formed from plates and fins and provided on at least one side surface in a stacking direction of the condensation passages and the evaporation passages , and one or more stages of the liquid reservoir section formed on at least one side surface of the heat exchanger core perpendicular to the stacking direction of the condensation passages and the evaporation passages so as to correspond with a number of stages of the evaporation passages . a heat exchanger core comprising (i) a heat exchange section formed by adjacently stacking the condensation passages and the evaporation passages formed from plates and fins standing next to each other, and (ii) a liquid communication section formed from the liquid communication passages which are formed from plates and fins and provided on at least one side surface in a stacking direction of the condensation passages and the evaporation passages , and one or more stages of the liquid reservoir section formed on at least one side surface of the heat exchanger core perpendicular to the stacking direction of the condensation passages and the evaporation passages so as to correspond with a number of stages of the evaporation passages . <EOS>