PURPOSE: To improve the wetting property of a lower stage side heat transfer tube, in which the transfer liquid is effected in later half after receiving the liquid from an upper stage side by a plurality of times and wetting is readily becomming uneven generally while bad effect due to the vertical deviation of the axis of tube is readily generated.

CONSTITUTION: A pair tube, having a flat surface 3, is employed for heat transfer tubes 1A-1J positioned at an upper stage side among 20 pieces of heat transfer tubes 1A-1J provided in an evaporator 5 or an absorber 6 while a shot- blasted tube, on the surface of which a non-directional rough surface 4, produced by shot-blasting treatment for spreading dropped liquid into four directions, is formed, is employed for heat transfer tubes 1K-1T positioned at a lower stage side.