NOVELTY - Gas (A) containing hydrogen is manufactured from raw material for hydrogen production by modification reaction in modifier (11), and carbon dioxide in gas (A) from modifier is absorbed using carbon dioxide absorber (1) during hydrogen production. Line comprising modifier and absorber is made into closed space at time of retardation. Carbon dioxide is discharged from absorber. Thus, operation of hydrogen-production apparatus is carried out.    USE - For operating hydrogen-production apparatus for producing hydrogen-containing gas used as fuel for fuel cell system (claimed) such as polymer electrolyte fuel cell used for moving components such as motor vehicles, fixing electric-power generation system and co-generation system for generating electric power.    ADVANTAGE - The hydrogen-production apparatus is operated, without degradation by oxidation of catalyst in hydrogen-production apparatus and performing purging at the time of retardation of fuel cell system.    DETAILED DESCRIPTION - The gas (A) containing hydrogen is manufactured from raw material for hydrogen production by modification reaction in a modifier (11), and carbon dioxide in the hydrogen-containing gas (A) from downstream of modifier is absorbed using absorption and dischargeable carbon-dioxide absorber (1) during hydrogen production. Line comprising modifier and carbon-dioxide absorber is made into closed space at the time of retardation. The carbon dioxide is discharged from the carbon-dioxide absorber. Thus, operation of hydrogen-production apparatus is carried out. INDEPENDENT CLAIMS are included for the following:    (1) hydrogen-production apparatus;    (2) operating method of fuel-cell system; and    (3) fuel-cell system.    DESCRIPTION OF DRAWING(S) - The figure shows the flowchart of the outline of the hydrogen-production apparatus. (Drawing includes non-English language text).    carbon-dioxide absorber (1)    modifier (11)    shift-reaction device (12)    selective-oxidation reactor (13)    valve (103)