a heat exchanger for exchanging heat with gas made to flow in a flow direction is disclosed . the heat exchanger is provided with : a plurality of plates each having a first side and a second side ; a plurality of tubes configured to conduct a thermal medium , the tubes penetrating the plates and being arranged in parallel with each other and on a plurality of planes perpendicular to the flow direction , wherein the tubes on each plane are disposed adjacent to gaps between the tubes on any of adjacent planes so as to form a plurality of serpentine flow lines among the tubes ; and a plurality of bridges projecting on the first sides of the plates , the bridges being respectively arranged to be perpendicular to the serpentine flow lines .