NOVELTY - A hydrogen generating apparatus (100) has a modifier (6) for producing a hydrogen-containing gas by reforming reaction using a raw material and water vapor, a material supply device (2), a water vapor supply device, a combustor (8), an air supply device (10), emitted-heat amount detector (12) and a target value setter (50). Based on the value detected in detector, setter sets at least one of target value of feed rate of raw material, target value of feed rate of water vapor, and the target value of feed rate of the combustion air, from target value of hydrogen generation amount.    USE - Hydrogen generating apparatus used in fuel cell system (claimed).    ADVANTAGE - The hydrogen generating apparatus is stably operated.    DETAILED DESCRIPTION - A hydrogen generating apparatus has a modifier for producing a hydrogen-containing gas by reforming reaction using a raw material and water vapor, a material supply device for supplying raw material to the modifier, a water vapor supply device for supplying water vapor to the modifier, a combustor for burning hydrogen-containing gas discharged from the modifier, and heating the modifier, an air supply device for supplying a combustion air to the combustor, emitted-heat amount detector for detecting the emitted-heat amount of the combustor when producing hydrogen-containing gas in the modifier, and a target value setter (50). Based on the value detected in emitted-heat amount detector, the target value setter sets at least one of target value of feed rate of the raw material to the modifier, the target value of feed rate of the water vapor to the modifier, and the target value of feed rate of the combustion air to the combustor, from the target value of the amount of hydrogen generation. An INDEPENDENT CLAIM is included for fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows the schematic view of hydrogen generating apparatus. (Drawing includes non-English language text)    Material Supply device (2)    Modifier (6)    Combustor (8)    Air supply device (10)    Emitted-heat amount detector (12)    Target value setter (50)    Hydrogen generating apparatus (100)