A steam reforming system with high thermal efficiency, which can compensate for a reduction in the amount of steam generated in a reformer without increasing the reformer size and without limiting the degree of freedom in layout of the reformer and a gas turbine. A gas turbine and a heat recovery exchanger are additionally installed such that the gas turbine generates electric power, and flue gases of the gas turbine are employed to preheat feedstocks supplied to the reformer and to generate steam used for the pre-reforming stage. The heat recovery exchanger is disposed in a downstream channel for the flue gases (at 500-600° C.) of the gas turbine to perform heat exchange between the high-temperature flue gases of the gas turbine and the feedstocks supplied to the reformer, thereby increasing the temperature of the feedstocks to a level suitable for vaporization and desulfurization, and to a level suitable for the pre-reforming stage in a pre-reformer. Generation and superheating of steam required for the pre-reforming stage are performed by the remaining heat of the flue gases of the gas turbine.