To provide a multiple heat exchanger and a method of assembling the same, of which the assembly in a field is easy and the assembling processes are simplified.

A shop-fabricated tube bank block W is constructed such that a plurality of cooling pipes 6 which are built between tube plates 8 are inserted into and supported by a plurality of pipe support plates 3 which are disposed in the longitudinal direction of the pipes with a given interval therebetween, that a plurality of reinforcing pipes 7 which are disposed at the outer periphery of the plates 3 are inserted into and supported by the plates, and that a plurality of H-shaped steel parts 2 which are located below the plates 3 and extended in the longitudinal direction of the pipes are detachably fixed to a lower portion of the plates 3 in the direction that crosses at right angle to the longitudinal direction of the pipes. The block W is transferred and conveyed into the body of a heat exchanger which has been set up in the field in advance, and assembled after the steel parts 2 are detached.