PURPOSE: To obtain a condensor/evaporator, capable of making the depth of liquid shallow while securing a sufficient heat transfer area and capable of manufacturing the same while employing manufacturing techniques so far without modification.

CONSTITUTION: An oxygen chamber, evaporating liquefied oxygen, is formed in a vertical direction, in which the upper end and the lower end of an evaporating flow passage are opened. A nitrogen chamber 30, condensing nitrogen gas, is divided into two condensing flow passages 32, 33 while inlet headers 32a, 33a for introducing nitrogen gas and outlet headers 32b, 33b for sending liquefied nitrogen out are provided on both sides of respective condensing flow passages 32, 33. The condensing flow passages 32, 33 of the nitrogen chamber are formed in the down slope of 45° or less with respect to the flow direction of the fluid.