Abstract: A reforming apparatus for hydrocarbon includes a first annular passage forming an outside stock gas passage filled with a catalyst. A second annular passage is arranged just inside of the first annular passage and in concentric relationship therewith to form an outside reformed gas passage. A third annular passage is arranged just inside of the second annular passage, and is connected thereto via a third communicating portion, for forming an inside reformed gas passage. A fourth annular passage is arranged just inside of the third annular passage and is connected between the first and third annular passages by first and second communicating portions, respectively, for forming an inside stock passage filled with the catalyst for reforming the stock gas. A first combustion gas passage is formed just inside of the fourth annular passage and a second combustion gas passage is formed just outside of the first annular passage, for heating the fourth and first annular passages, respectively.