NOVELTY - A hydrogen generating apparatus (100) has a reforming reaction device (2), a transformation reactor (3), a selective oxidation reactor (4), and a space (106) which moves catalyst to at least one of upper portion of reforming reaction device, transformation reactor and selective oxidation reactor. The running of hydrogen generating apparatus is stopped, installation of the apparatus is changed, and catalyst is moved. The installation state of apparatus is returned to the original state. Thus, maintenance of hydrogen generating apparatus is enabled.    USE - Method for maintaining hydrogen generating apparatus used for generating hydrogen rich gas for polymer electrolyte fuel cell.    ADVANTAGE - The deterioration of catalyst after long period of usage is prevented. The start-stop of hydrogen generating apparatus is frequently repeated. The durability of hydrogen generating apparatus is improved. The hydrogen gas is obtained with low carbon monoxide concentration.    DETAILED DESCRIPTION - A hydrogen generating apparatus has a reforming reaction device, a transformation reactor, a selective oxidation reactor, and a space which moves catalyst to at least one of upper portion of reforming reaction device, transformation reactor and selective oxidation reactor. The reforming reaction device has a modification catalyst (2a) for reform-reacting a raw material and water, and producing hydrogen-containing gas. The transformation reactor has a transformation catalyst (3a) for carrying out transformation of carbon monoxide in hydrogen-containing gas. The selective oxidation reactor has a selective oxidation catalyst (4a) which carries out selective oxidation of carbon monoxide contained in hydrogen-containing gas. At least one of modification catalyst, transformation catalyst and selective oxidation catalyst is a pellet-type catalyst. The running of hydrogen generating apparatus is stopped, installation of the apparatus is changed, and catalyst is moved. The installation state of apparatus is returned to the original state. Thus, maintenance of hydrogen generating apparatus is enabled.    DESCRIPTION OF DRAWING(S) - The drawing shows the block diagram of hydrogen generating apparatus. (Drawing includes non-English language text)    Reforming reaction device (2)    Modification catalyst (2a)    Transformation reactor (3)    Transformation catalyst (3a)    Selective oxidation reactor (4)    Selective oxidation catalyst (4a)    Hydrogen generating apparatus (100)    Space (106)