NOVELTY - A hydrogen producing apparatus (31) comprises 1st desulfurization part (1) which removes sulfur compound in supplied source gas at normal temperature, 2nd desulfurization part (2) which is positioned downstream and reacts sulfur compound in source gas and hydrogen, modification part (3) which reforms source gas from 2nd desulfurization part to reformed gas containing hydrogen, recycle line (21) for mixing with source gas which branches in downstream from modification part and supplies part of reformed gas from modification part to 2nd desulfurization part, and desulfurization line (22).    USE - A hydrogen producing apparatus for supplying hydrogen-containing gas to domestic fuel cell system.    ADVANTAGE - Deterioration of modification catalyst which causes poisoning can be prevented, and hydrogen producing apparatus can be continuously operated.    DETAILED DESCRIPTION - A hydrogen producing apparatus (31) comprises 1st desulfurization part (1) which removes sulfur compound in supplied source gas at normal temperature, 2nd desulfurization part (2) which is positioned downstream and reacts sulfur compound in source gas and hydrogen, modification part (3) which reforms source gas from 2nd desulfurization part to reformed gas containing hydrogen, recycle line (21) for mixing with source gas which branches in downstream from modification part and supplies part of reformed gas from modification part to 2nd desulfurization part, desulfurization line (22) for supplying source gas to 2nd desulfurization part via 1st desulfurization part, bypass line (23) for supplying source gas to 2nd desulfurization part, without going through 1st desulfurization part, orifice (11) positioned at recycle line, obstruction detection part (6) which is positioned downstream from orifice and detects obstruction of recycle line, valve (12) which is positioned downstream from orifice and carries out conduction and interruption of recycle line, and switch part (7) which switches desulfurization line and bypass line. When source gas is supplied to 2nd desulfurization part through bypass line and obstruction detection part detects obstruction, switch part switches path of source gas to desulfurization line.    DESCRIPTION OF DRAWING(S) - The drawing shows a block diagram of the hydrogen producing apparatus. (Drawing includes non-English language text).    1st desulfurization part (1)    2nd desulfurization part (2)    Modification part (3)    Obstruction detection part (6)    Switch part (7)    Orifice (11)    Valve (12)    Recycle line (21)    Desulfurization line (22)    Bypass line (23)    Hydrogen producing apparatus (31)