A hydrogen generator using steam reforming, having a desulfurizer for desulfurizing a hydrocarbon feed; a reformer for performing a steam-reforming reaction of the mixture of desulfurized hydrocarbon feed and a water feed by heating the mixture using a burner to form a reformed gas; a water gas converter for converting carbon monoxide in the reformed gas obtained from the reformer into a converted gas of hydrogen (H 2) and carbon dioxide (CO 2); and a pressure swing absorption unit for separating hydrogen (H 2) from the converted gas; characterized in that the hydrogen generator comprises: a first heat exchanger for superheating the water feed to 180 to 220°C, which is higher than an evaporation temperature of water, through heat exchange with the exhaust gas discharged from the burner to convert the water feed into a single-phase vapor before the water feed is mixed with the desulfurized hydrocarbons, thereby forming a mixture of the desulfurized hydrocarbon feed and the superheated water, wherein the ratio of steam to carbon in said mixture is in a range of 2.5 to 3.5; a second heat exchanger for preheating the mixture of the desulfurized hydrocarbon feed and the superheated water through heat exchange with the reformed gas discharged from the reformer, whereby the superheated water is introduced into the reformer in such a state that a single vapor phase is maintained without phase separation of water; a third heat exchanger for decreasing a temperature of the reformed gas through heat exchange with external air before the reformed gas is introduced into the water gas converter; and a fourth heat exchanger for additionally decreasing a temperature of the gas discharged from the water gas converter through heat exchange with tap water before the converted gas is introduced into the PSA unit, wherein each of the first, second, third and fourth heat exchangers is a finned tube type heat exchanger or a shell and tube type heat exchanger. a first heat exchanger for superheating the water feed to 180 to 220°C, which is higher than an evaporation temperature of water, through heat exchange with the exhaust gas discharged from the burner to convert the water feed into a single-phase vapor before the water feed is mixed with the desulfurized hydrocarbons, thereby forming a mixture of the desulfurized hydrocarbon feed and the superheated water, wherein the ratio of steam to carbon in said mixture is in a range of 2.5 to 3.5; a second heat exchanger for preheating the mixture of the desulfurized hydrocarbon feed and the superheated water through heat exchange with the reformed gas discharged from the reformer, whereby the superheated water is introduced into the reformer in such a state that a single vapor phase is maintained without phase separation of water; a third heat exchanger for decreasing a temperature of the reformed gas through heat exchange with external air before the reformed gas is introduced into the water gas converter; and a fourth heat exchanger for additionally decreasing a temperature of the gas discharged from the water gas converter through heat exchange with tap water before the converted gas is introduced into the PSA unit, wherein each of the first, second, third and fourth heat exchangers is a finned tube type heat exchanger or a shell and tube type heat exchanger.