To provide a heat exchanger wherein replacing or repairing a broken tube is able to be conducted simply when a part of tubes for heat exchange is broken.

Tube units 2 are formed, wherein heat exchange tubes 1 are formed into zigzag shapes by a plurality of straight pipe parts and folded pipe parts so as for a first fluid to flow inside of the heat exchange tubes 1, and plural numbers of the heat exchange tubes 1 are integrally framed in parallel in a direction crossing a flowing direction of the first fluid at a right angle. A plurality of the tube units 2 are fabricated and disposed in a multi-stage shape so that each of flow outlets 6a and each of flow inlets 7a of each of the tube units 2 are provided oppositely inside a heat exchanger body 3 through which a second fluid flows. Each of the flow outlets 6a and each of the flow inlets 7a of each of the tube units 2 provided oppositely are detachably communicated with and connected with each other by each of connecting tubes 10.