NOVELTY - An autothermal reformer (ATR) (1) comprises a reaction container (12) having first opening (13a) through which fuel is introduced into reaction container and second opening (13b) through which reformate is discharged from reaction container; a first granular catalyst (20) adjacent to first opening; a second catalyst (30) at a rear portion of first catalyst to promote an autothermal reforming reaction; and a third catalyst (40) at a rear portion of second catalyst to promote an oxidation reaction. The fuel comprises mixture of aqueous primary fuel solution and hydrogen peroxide.    USE - Autothermal reformer used for a fuel cell system (claimed).    ADVANTAGE - The ATR has high performance and high efficiency, and is small and inexpensive and capable of performing reproducible ignition using a catalyst layer that performs ignition without a separate ignition unit (e.g. igniter or heating wire). Further, performance such as reduction of starting time can be improved, and an amount of air additionally supplied for ignition can be omitted, so that power consumption can be saved in the start of a system, and the capacity and volume of a subsidiary power source such as a secondary battery can be reduced.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a fuel cell system, comprising a fuel tank to store a fuel in which an aqueous primary fuel solution and hydrogen peroxide are mixed together; the ATR which receives the fuel supplied from the fuel tank, starts through self-ignition, and produces a reformate by reforming the fuel; a carbon monoxide reducing unit disposed at the rear portion of the ATR to reduce the concentration of carbon monoxide of the reformate; an electric generation unit to generate electricity by receiving hydrogen supplied from the carbon monoxide reducing unit and allowing the hydrogen to electrochemically react with oxygen; and a control unit to control the amount and composition of the fuel supplied to the ATR.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the ATR.    ATR (1)    Reaction container (12)    First opening (13a)    Second opening (13b)    First granular catalyst (20)    Second catalyst (30)    Third catalyst (40)