PURPOSE: To increase a heat exchanger area by allowing a fluid and a heat medium to heat-change therebetween via a plurality of heat transfer pipes through porous structures in those heat transfer pipes by constructing a title evaporator as a multiple pipe type heat exchange structure in which the porous structures each having cavities opening toward end surfaces on the outlet side of evaporated gas are inserted into the heat transfer pipes into each of which the fluid flows.

CONSTITUTION: A pair of an upper pipe plate 41 and a lower pipe plate 42 are disposed at the middle portion of a trunk of a container 40, and a plurality of heat transfer pipes 43 are supported on the upper and lower pipes plates 41, 42. Into each heat transfer pipe 43 a porous structure 45 having a circular hole-shaped cavity 44 opening toward the lower end of a title evaporator is inserted. The porous structure 45 is formed from a sintered product of metal particles. Heat exerted on the heat transfer pipe 43 by heating is transmitted to the porous structure 45 to evaporate a modified stock material entering the porous structure 45 into modified stock material gas as evaporated gas which gas in turn passes through the cavity 44 of each porous structure, and is collected in a mirror plate part and is sent from an outlet pipe top the outside, i.e., to a fuel refiner.