NOVELTY - A heater (3) heats a main container (2A) stores a sub catalyst (Rb) and a secondary catalyst layer (R2) of a main catalyst (Ra). A heater (H) heats an auxiliary container (2B) stores a primary catalyst layer (R1) of the main catalyst. The valves (10,11) selectively switch the flow of fuel between initial operation mode and steady operation mode of the fuel reformer.    USE - For reforming fuel, such as natural gas, methane, or liquefied petroleum gas, to produce hydrogen-rich reformed gas used in fuel cell for electric power generation.    ADVANTAGE - Enables producing heat by the reaction between the fuel and the oxidizing gas, during starting of the reformer, and utilizing the heat for heating the secondary catalyst layer and the sub catalyst, without the use of a separate heat source. Since water vapor is passed through the catalysts, after the catalysts are heated, the water vapor is heated efficiently so that the reformed gas is produced stably and continuously. Enables producing water vapor by heating the water vapor generator using the heat of the catalysts. Enables transferring the primary catalyst layer to the auxiliary container, so as to efficiently heat the primary layer, independent of the other catalyst layers, hence enables accurately controlling the temperature of the primary layer.    DETAILED DESCRIPTION - The fuel and an oxidizing gas are passed through the primary and secondary catalyst layers of the main catalyst and the sub catalyst, in order, during starting of the reformer. The reformer is switched to steady operation, by passing the fuel and water vapor through main and sub catalysts, in order, or bypassing the primary catalyst and passing through the remaining catalysts, when oxidizing gas supply is stopped. The reformer has a detector to detect whether the primary catalyst layer has reached a preset temperature. The auxiliary heater heats the primary layer. A controller (14) enables starting the reformer, when the detected temperature matches with the preset temperature. The fuel is switched to steady operation mode, when the detected temperature of the sub catalyst matches a preset temperature.    DESCRIPTION OF DRAWING(S) - The figure shows a longitudinal sectional view of the reformer. (Drawing includes non-English language text).    main and auxiliary containers (2A, 2B)    heater (3, H)    valves (10,11)    controller (14)    primary and secondary catalyst layers (R1, R2)    main catalyst (Ra)    sub catalyst (Rb)