NOVELTY - A fuel reforming device (D1) comprises a reformer to generate reformate gas having hydrogen as main component according to a catalytic reaction of several materials (m1) including a hydrocarbon fuel; a first (1) and second (2) carbon monoxide oxidizer; a heating mechanism; an oxygen supply mechanism; and an adjusting mechanism which varies an oxygen supply amount to (1) and (2).    USE - To generate hydrogen-rich gas from hydrocarbon fuel (claimed) e.g. gasoline and methanol, used by fuel cell stack.    ADVANTAGE - The heating of the material supplied to the reformer can be enhanced with a sufficient response to the increase in the fuel-reforming requirement of the reformer, regardless of the running state of the fuel cell stack by increasing the air supply proportion to the first carbon monoxide oxidizer. Also, the high temperature water amount supplied to the reformer can be increased with a sufficiently good response according to the increase in the fuel reforming requirements. Thus, the device has desirable effect particularly in application to a fuel cell vehicle where the fuel-reforming requirement changes frequently. No heat is wasted and reforming efficiency is also high.    DETAILED DESCRIPTION - A fuel reforming device (D1) comprises a reformer (8) to generate reformate gas (g1) having hydrogen as main component according to a catalytic reaction of several materials (m1) including a hydrocarbon fuel; a first (1) and second (2) carbon monoxide oxidizer to decrease a carbon monoxide concentration of (g1) by oxidizing carbon monoxide in (g1) by a preferential oxidation using oxygen; a heating mechanism (6,7, 12,13, 15a, 15b, 16,17a, 17b, 17c) which heats any of (m1) using a preferential oxidation heat of (1); (2) is disposed in series with (1); an oxygen supply mechanism (9, 10b, 10c, 10d) which supplies oxygen to (1) and (2); and an adjusting mechanism (4,5) which varies an oxygen supply amount to (1) and to (2).    DESCRIPTION OF DRAWING(S) - The figure shows a fuel reforming device.    a reformer (8)    first carbon monoxide oxidizer (1)    second carbon monoxide oxidizer (2)    a heating mechanism (6,7, 15a, 15b)    oxygen supply mechanism (9, 10b, 10c, 10d)    an adjusting mechanism (4,5)    controller. (11)