TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Component: The fuel reformer further comprises a carbon monoxide reduction unit constructed by filling another region of the space between the first and second pipes with a water gas shift catalyst to reduce a concentration of carbon monoxide contained in the reforming gas; and a mesh-shaped barrier disposed between the pipes to partition the space between the pipes into the region filled with the reforming catalyst and the another region filled with the water gas shift catalyst.A preheating unit is disposed in the reactor body (50) to ignite and burn the first reactant in order to preheat the reactor body. The preheating unit comprises a housing for enclosing the reactor body; and a burner disposed in the housing to ignite and burn the first reactant external to the reactor body. The reformer comprises first reaction substrates including first channels for allowing a first reactant including a fuel to flow and in which an oxidation catalyst layer formed on a surface of the first channels; and one or more second reaction substrates including second channels for allowing a second reactant including the fuel to flow and a reforming catalyst layer formed on a surface of the second channels. The reactor body includes a cover plate adhered to the second reaction substrate of one of the unit bodies.The housing comprises a first portion having a horn shape located at a first end portion of the reactor body; a second portion having a horn shape located at a second end portion of the reactor body; and a third portion adhered to the reactor body with the exception of the first end portion of the reactor body and the second end portion of the reactor body. The housing comprises an injection hole for injecting the first reactant into the first portion formed in the first portion, and a discharging hole for discharging a combustion gas of the first reactant burned by the burner and a reaction gas of the first reactant oxidized by the oxidation catalyst layer is formed in the second portion.