A hydrogen generator having a reforming catalyst that causes hydrocarbon gas and steam to carry out a reforming reaction and reform into a hydrogen rich reformed gas, a reformer that is filled with said reforming catalyst and in which said reforming reaction is carried out, and a combustion chamber for combusting a fuel gas and obtaining reaction heat that is applied to said reforming reaction. At least the reforming region carrying out the reforming reaction is disposed inside the combustion chamber. A steam generator that introduces steam into the reformer is provided outside the combustion chamber.