A small cylindrical reformer according to the embodiments of the present invention are suitable for use in the production of hydrogen from fossil fuels for a small fuel cell power plant. In the small cylindrical reformer, a reforming reactor, a water gas shift reactor (high temperature or low temperature), a combustor, a heat exchanger, a steam generator, etc., may be integrated in a single container to form an optimal heat exchanging network, minimize heat loss and optimize heat exchange efficiency. Thereby, the reformer is designed to be easily processed and manufactured and to have a compact size, thus realizing high efficiency, light weight and ease of mass production.