A reformer which comprises: a reforming vessel (152) having a reforming c hamber (152C) formed therein which is an almost annular space to be packed w ith a reforming catalyst; a heating means disposed so as to be located nearl y on the center axis of the reforming vessel (152); and a flow part (153) co nstituted of two or more double-tube structures (153C) which each comprises a feed tube (153A) which is connected to one axial-direction end of the refo rming vessel (152) and supplies a feed gas to one axial-direction end side o f the reforming chamber (152C) and a return tube (153B) fitted into the corr esponding feed tube (153A) almost coaxially. One end of the return tube pier ces the reforming chamber (152C) and is open at the other axial-direction en d side of the reforming chamber (152C) so that a reformed gas generated by r eforming the feed gas with the reforming catalyst can flow into. This reform er has a simple structure and enables efficient and stable reforming.</SDOAB >
