PURPOSE: To form block into a pipeless structure and unrequire the pipeline connection of the outside of the block by laminating first and second blocks, communicating inlet and outlet ports of these blocks with through-holes thereby to form four main current lines, and making opening ends of respective main current lines outlet and inlet ports of a heat exchange medium.

CONSTITUTION: A first block 1 flowing a fluid for a heat source and a second block 2 flowing a fluid for a heat source to be heated are laminated to form a unit heat exchange unit A. The first block 1 provides upright a partitioning part 6 on a thin passage wall 5 to form a first zigzag passage 7. On the other hand, the second block 2 provided upright a partitioning part 24 on a thin passage wall 23 to form a second zigzag passage 25. At the left lower corner of the second block is formed a second inlet port 28 communicating with the second zigzag passage 25 by a perforated hole 26 and a discontinuous annular rib 27, and the second inlet port 28 is faced with the first through hole 17 of the first block 1.