NOVELTY - The apparatus (1) has the DC power supplies (A-C) that are provided to supply electric power parallelly with respect to a cell stack block (10) and connected to the cathode and anode side terminal portions (11,17) located in the end portions of cell stack block at the cathode and anode sides respectively. The DC power supplies are respectively connected with the electrode portions (12-16) locating the anode and cathode side terminal portions of block at the anode and cathode sides, and between each cell stack parallelly through the relays (a1-a6,b1-b6,c1-c6) respectively.    USE - Apparatus for producing hydrogen using solid polymer form water electrolysis cell and reversible cell.    ADVANTAGE - The DC power supplies are respectively connected with the electrode portions locating the anode and cathode side terminal portions of cell stack block at the anode and cathode sides, and between each cell stack parallelly through a relay respectively so that electric power is supplied with respect to all the cells without equipping the constant voltage power source for exclusive use exceptionally even when the energy used as the output source of power supply falls when the power supply derived from a renewable energy is used as electric power supply source for electrolysis. Thus, the largest electric power at that time for electrolysis operation is utilized effectively according to the fluctuation of energy. Hence, the hydrogen concentration raise at the side of oxygen by the generation of cell to which the electrolysis operation is not performed is prevented effectively without the need of constant voltage power source for exclusive use.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a method for operating hydrogen production apparatus.    DESCRIPTION OF DRAWING(S) - The drawing shows an explanatory view of the hydrogen production apparatus.    Apparatus for producing hydrogen (1)    Cell stack block (10)    Cathode and anode side terminal portions (11,17)    Electrode portions (12-16)    DC power supplies (A-C)    Relays (a1-a6,b1-b6,c1-c6)