A hydrogen generator of the present invention is provided with: a reformer for generating a reformed gas containing hydrogen from a feed material containing an organic compound at least containing carbon and hydrogen and water; a heater for heating the reformer to a temperature required for generating the reformed gas; a carbon monoxide reducing unit having a carbon monoxide reducing catalyst for reducing carbon monoxide contained in the reformed gas generated in the reformer; and a temperature detector for detecting at least one of a temperature of the reformed gas in the carbon monoxide reducing unit and a temperature of the carbon monoxide reducing catalyst, wherein an amount of the feed material to be supplied to the reformer is controlled based on a comparison between a detected temperature detected by the temperature detector and a reference temperature set in accordance with the amount of the feed material.