A hydrogen generation device or a fuel cell system of the present invention can prevent deterioration or breakage of portions of the hydrogen generation device, which is caused by thermal stress attributable to repeated operation and halt. Thus, it is possible to increase the life and enhance the stability of the device and the system.A hydrogen generation device 76 of a fuel cell system 100 includes a hydrogen generation device main body 78 including a combustor 4 provided therein for combusting a predetermined medium capable of generating hydrogen and a plurality of pipes which are connected to the hydrogen generation device main body 78 for allowing the predetermined medium flow into or out of the hydrogen generation device main body 78. A temperature gradient is formed in the hydrogen generation device main body 78 by operation of the combustor 4, whereby a high temperature portion and a low temperature portion are formed in the hydrogen generation device main body 78. All of the plurality of pipes are arranged in the low temperature portion. A support 70 supports the hydrogen generation device main body 78 from an outside of the low temperature portion.