A reformer that includes a housing including a tubular member and an end plate member hermetically joined to the tubular member. The housing defines within it a first fluid flow path and a second fluid flow path in a heat exchanging relationship with each other. A reforming catalyst is disposed within the first fluid flow path. The tubular member has a tubular end, and the end plate member has an abutting rim that contacts with and extends along the tubular end of the tubular member and that is folded together over an entire circumference thereof to define a folded hermetic seam between the tubular member and the end plate member. The reformer can be low-priced and its manufacture is easy and efficient.