The present specification discloses a hydrogen generator for generating a hydrogen gas, comprising at least a fuel supply part for supplying a hydrocarbon type fuel, a fuel combustion part, a water supply part, a gas, mixing part for mixing the fuel and a water, and a reforming part filled with the reforming catalyst, wherein at least one of the gas mixing part and the reforming part is heated by an exhaust gas generated in the combustion part. The hydrogen generator according to the present invention aims to improve the heat efficiency, reducing the heat loss from the apparatus with a simple constitution and collecting the waste heat for an effective use thereof.