Abstract: In a combustion gas reformer, exhaust ducts are provided at a lower portion of the reformer. Openings are provided in opposite side walls along the length of each exhaust duct. The openings are uniformly distributed at a constant height along the longitudinal direction of the exhaust duct. The openings are disposed in the side walls at a constant height, and may be arrayed in two steps or rows. A partition wall is provided on the upper wall and extends along the length of the exhaust duct. The amount of combustion gas flowing into the duct through the openings at the lower portion of the side walls increases gradually toward the exhaust outlet. However, since the cross section of the duct toward the outlet becomes gradually enlarged, pressure and gas distribution become uniform. Also, no transverse flow of the combustion gas occurs, due to the partition wall being disposed on the upper wall of the duct.