NOVELTY - Starting a modifier of an inside heating type of an autooxidation, comprises providing a mixed catalyst layer (6), which mixed a modification catalyst and an oxidation catalyst with a main reforming/modification chamber (3). High temperature gas is supplied to the mixed catalyst layer from a first preheater at the time of starting. High temperature gas is further supplied to a supply part (4) of an outside preliminary/backup reforming/modification chamber (2) from a second preheater (21) (equipped with oxidation-catalyst layer (23)) at the time of starting.    USE - For starting a modifier of an inside heating type of an autooxidation, useful for generating hydrogen for fuel cell.    ADVANTAGE - The method of starting rapidly is provided without heat-retaining. A shift catalyst layer is heated up to an operating temperature directly and quickly by the high temperature gas which flows out of the indirect heating from a preliminary/backup reforming/modification chamber, and a preliminary/backup reforming/modification chamber at the time of starting. Even if dew condensation arises during the stop of the modifier at a shift catalyst layer, the dew condensation will be rapidly removed at the time of starting. The starting time of the modifier can be shortened. High temperature gas can be easily produced or generated. A structure of a reforming/modification system becomes simpler and a driving/running also becomes easy.    DETAILED DESCRIPTION - Starting a modifier of an inside heating type of an autooxidation, comprises providing an inside main reforming/modification chamber and an outside preliminary/backup reforming/modification chamber; providing a supply part and a modification-catalyst layer (5) of a raw material-water-vapor/steam mixture in the preliminary/backup reforming/modification chamber; and providing a shift catalyst layer (7) and hydrogen-rich reformed gas. A discharge part (10) of a mixed catalyst layer, which mixed the modification catalyst and the oxidation catalyst with the main reforming/modification chamber, is provided. High temperature gas is supplied to the mixed catalyst layer from a first preheater at the time of starting. High temperature gas is further supplied to the supply part of the preliminary/backup reforming/modification chamber from a second preheater at the time of starting.    DESCRIPTION OF DRAWING(S) - The figure is a sectional drawing in which the modifier of the inside heating type/mold of an autooxidation is shown. (Drawing includes non-English language text).    Outside preliminary/backup reforming/modification chamber (2)    Main reforming/modification chamber (3)    Supply part (4)    Modification-catalyst layer (5)    Mixed catalyst layer (6)    Shift catalyst layer (7)    Discharge part (10)    Second preheater (21)    Oxidation-catalyst layer (23)