PURPOSE: To prevent the breakage of a reforming catalyst due to the thermal deformation of a reformer tube at the start-up by providing an expansion bend capable of compensating for a reduction in the volume of a catalyst bed space due to the difference in thermal expansion between an inner cylinder and an outer side wall on the outer side wall of the fuel reformer.

CONSTITUTION: An outer casing 7 consisting of an upper outer cylinder 5 surrounding an inner cylinder 1 through an upper plate 3 which is annular at its lower end and a lower plate 4 and a lower outer cylinder 6 is connected to the inner cylinder 1, and an outer cylinder 2 as the outer side wall surrounding the inner cylinder 1 is provided between the inner cylinder 1 and the outer casing 7 away from the upper plate 3 and lower plate 4. Both ends of the inner cylinder 1 and outer cylinder 2 are opened. A corrugated plate 30 consisting of a puckered bend extending in the axial direction of the outer cylinder 2 is provided to the outer cylinder 2. A reformer tube 11 contg. the bed 10 of a reforming catalyst 9 is formed in the space 8 between the inner cylinder 1 and the outer cylinder 2, and a burner 22 is furnished inside the inner cylinder 1. A heating medium is supplied into the inner cylinder 1 from the burner 22 to heat the reformer tube 11, and the hydrocarbonic fuel passing through the catalyst bed 10 is steam-reformed into a gas enriched with hydrogen.