A heat exchange section (1) composed of a fuel supply part (7); core (5), and steam collecting part (9). A heat exchange section (1) composed of the fuel supply part (7), core (5) and steam collecting part (9) is secured to a side wall plate (37). Three faces of the heat exchange section (1) except for the side wall plate side, high temperature gas inlet side and outlet side are covered by the housing body (43). Heat resistant filler (45), intervenes between the housing body (43) and the heat exchange section (1). An upper and lower portions (43b, 43c) of the housing body (43) are prevented from deforming due to thermal expansion of the core (1) by a heat deformation absorbing mechanism (47) which is formed by bending the joint of the flange (43a) of the housing body (43) and an upper and lower end portions (37a) of the side wall plate (37).