A hydrogen generator according to the invention comprises: a combustion gas passage (5) configured to flow combustion gas coming from a combustor; a preheat-evaporator (6) which is supplied with a material gas and water and configured to evaporate the water and heat the material gas by heat transmitted from the combustion gas passage and a carbon monoxide reducer (10) through partition a wall; a reformer (7) configured to generate reformed gas from the material gas and steam fed from the preheat-evaporator by using a reforming catalyst (8) and heat transmitted from the combustion gas passage through the partition wall; the carbon monoxide reducer (10) configured to remove carbon monoxide from the reformed gas fed from the reformer by a carbon monoxide removing catalyst (9); a cylindrical body (3) closed at both ends thereof having an internal space is divided by the partition walls (1), (2), (30), (47) to form the combustion gas passage, preheat-evaporator, reformer and carbon monoxide reducer within the cylindrical body (3), wherein a heat transmission buffering section (11) is formed between the preheat-evaporator and the carbon monoxide reducer such that the partition wall (30) that defines the preheat-evaporator and the partition wall (47) that defines the carbon monoxide reducer are opposed to each other with a space therebetween.