Abstract: A heat exchanger is disclosed. A first heat-exchanging plate, in which plural kinds of cooling water are circulated, and a second heat-exchanging plate, in which refrigerant is circulated, have respective independent flow channels to prevent mixing between the cooling water and the refrigerant. The first and second heat-exchanging plates have respective guides, which are layered so as to form an overlapping structure, thereby improving coupling capability and durability when the first and second heat-exchanging plates are welded to each other in the state of being layered.