NOVELTY - The apparatus has thin plates laminated such that reformed-gas flow paths, water flow paths are formed alternately. Water supplied in opposite direction to the flow-direction of reformed-gas, is heated by reformed gas, and vaporized. Flow paths are connected so that water vapor produced in water flow paths, flows to gas flow paths. Distribution of water in the apparatus is made into a preset non-uniform state.    USE - For mixing water vapor with reformed gas, before supplying reformed gas to carbon monoxide removal unit of fuel reformer which produces hydrogen-rich heating gas to be supplied to fuel cell.    ADVANTAGE - Enables efficiently producing water vapor using the heat energy of the reformed gas, and efficiently mixing water vapor with reformed gas, without using a steam generator. Hence reduces the size of fuel reformer. Enables making the temperature distribution of the reformed gas which is supplied to the carbon-monoxide content reduction unit, uniform, by suitably setting the distribution state of water in the water-vapor mixing apparatus.    DETAILED DESCRIPTION - A water-supply manifold supplies water from exterior of the apparatus to the water flow paths. The preset non-uniform state is set such that the variation in the temperature distribution of reformed gas passing through the apparatus, is decreased, and the variation in the temperature distribution of the laminated plates, is decreased. The quantity of water supplied to each water flow path is made non-uniform. An INDEPENDENT CLAIM is also included for fuel reformer which has a reforming unit which produces a reformed gas containing hydrogen and carbon monoxide, from a fuel. A heat exchanger is provided for reducing the temperature of the reformed gas, to a preset value, before reformed gas is supplied into the water-vapor mixing apparatus. The water-vapor mixing apparatus has several laminated plates between which water flow paths and reformed-gas flow paths are formed. The reformer has a reaction unit which promotes a shift reaction of the reformed gas, using water vapor, to produce hydrogen and carbon dioxide, so as to reduce the concentration of carbon monoxide in the reformed gas.    DESCRIPTION OF DRAWING(S) - The figure shows a explanatory view of a water distribution manifold of a water-vapor mixing apparatus. (Drawing includes non-English language text).    laminated structure (17)    water flow path (18)    main channel (76)    branch flow paths (77,78)