Provided is a fuel reforming device, which can produce and supply a reformed gas in quick response to a demand for the reformed gas and which is so inexpensive as can be suitably mounted on a vehicle. The fuel reforming device feeds a material to a reforming catalyst and produces the reformed gas under a pressure higher than the atmospheric pressure. The fuel reforming device comprises a material supply means for supplying the material to the reforming catalyst, a reforming means having the reforming catalyst, for reforming the material supplied from the material supply means, to produce the reformed gas, and a run control means for controlling the run of the fuel reforming device. The run control means includes a stop mode, in which the drive of the material supply means is stopped to stop the production of the reformed gas, a reform mode, in which the material supply means is driven to produce the reformed gas, and a standby mode, in which the material supply means is driven and in which the temperature of the reforming catalyst is held within a predetermined range while producing the reformed gas as little as possible, so that the standby mode can shift instantly to the reform mode.