A hydrogen generator comprising: a material supply device for supplying material gas; a water supply device for supplying water; an evaporator for evaporating the water fed from said water supply device thereby to produce steam; a reforming catalyst layer having a reforming catalyst for generating hydrogen-containing reformed gas through a reforming reaction using said material gas and said steam; a CO removing catalyst layer configured to reduce the amount of carbon monoxide contained in said reformed gas generated by said reforming catalyst layer; a combustor for heating said reforming catalyst layer and said CO removing catalyst layer; a reforming temperature detector for detecting the temperature of said reforming catalyst layer; a heater for heating said CO removing catalyst layer; a CO removing temperature detector for detecting the temperature of said CO removing catalyst layer; and characterized in that a controller configured to perform control such that, prior to supplying of material gas and prior to heating of the reforming catalyst layer, said heater heats said CO removing catalyst layer at the time of start-up, and the controller is configured to perform control such that if the temperature detected by said CO removing temperature detector becomes greater than or equal to a first specified value, said material supply device begins to supply material gas and said combustor heats said reforming catalyst layer and said CO removing catalyst layer, and then if the temperature detected by said reforming temperature detector becomes greater than or equal to a second specified value, said water supply device starts supplying of water. a material supply device for supplying material gas; a water supply device for supplying water; an evaporator for evaporating the water fed from said water supply device thereby to produce steam; a reforming catalyst layer having a reforming catalyst for generating hydrogen-containing reformed gas through a reforming reaction using said material gas and said steam; a CO removing catalyst layer configured to reduce the amount of carbon monoxide contained in said reformed gas generated by said reforming catalyst layer; a combustor for heating said reforming catalyst layer and said CO removing catalyst layer; a reforming temperature detector for detecting the temperature of said reforming catalyst layer; a heater for heating said CO removing catalyst layer; a CO removing temperature detector for detecting the temperature of said CO removing catalyst layer; and characterized in that a controller configured to perform control such that, prior to supplying of material gas and prior to heating of the reforming catalyst layer, said heater heats said CO removing catalyst layer at the time of start-up, and the controller is configured to perform control such that if the temperature detected by said CO removing temperature detector becomes greater than or equal to a first specified value, said material supply device begins to supply material gas and said combustor heats said reforming catalyst layer and said CO removing catalyst layer, and then if the temperature detected by said reforming temperature detector becomes greater than or equal to a second specified value, said water supply device starts supplying of water.