Provided is a fuel processing device including a reforming unit and a combustion unit. The reforming unit includes a first tubular wall and a second tubular wall. A reforming reaction flow path is formed between the first tubular wall and the second tubular wall, the reforming reaction flow path being configured to allow the raw material and the reformed gas to flow through the reforming reaction flow path. A combustion gas flow path configured to allow the combustion gas to flow through the combustion gas flow path is formed on an inner peripheral side with respect to the first tubular wall. An outer peripheral flow path configured to allow an outer peripheral gas to flow through the outer peripheral flow path is formed on an outer peripheral side with respect to the second tubular wall. The fuel processing device further includes: a merging portion configured to allow the combustion gas having flowed through the combustion gas flow path and the outer peripheral gas having flowed through the outer peripheral flow path to merge with each other; an exhaust gas flow path configured to allow the combustion gas and the outer peripheral gas that have merged at the merging portion to flow through the exhaust gas flow path as an exhaust gas; an oxidizing agent flow path configured to allow an oxidizing agent supplied from a heating source to pass through the oxidizing agent flow path; an oxidizing agent branching portion provided in the oxidizing agent flow path; a combustion supporting gas flow path that connects between the oxidizing agent branching portion and the combustion unit and is configured to allow a part of the oxidizing agent to flow through the combustion supporting gas flow path as the combustion supporting gas; and an outer peripheral gas introducing flow path that connects between the oxidizing agent branching portion and the outer peripheral flow path and is configured to allow the other part of the oxidizing agent to flow through the outer peripheral gas introducing flow path as the outer peripheral gas.
