An apparatus includes: an electrolytic cell (6) having an electrolytic chamber (3) to which subject raw water (2) to be electrolyzed is introduced, at least one membrane (13) that partitions inside and outside of the electrolytic chamber, and at least a pair of electrode plates (4, 5) provided in the inside and the outside of the electrolytic chamber so as to sandwich the membrane, the electrode plate in the outside of the electrolytic chamber being provided to be in contact with the membrane a direct-current power source (14) that applies a direct-current voltage to the pair of electrode plates and a diluent gas supply means (10, 11) for supplying a diluent gas for diluting hydrogen gas generated from an electrode plate of the pair of electrode plates that is to be the cathode, wherein at least a part of a gas phase portion (7) formed in the electrolytic chamber is covered with a hydrogen gas permeable membrane (8), the apparatus blows diluent gas supplied using the diluent gas supply means to the cathode or a cathode water surface thereby to constantly maintain a hydrogen gas concentration in a position separated by 7 cm from the cathode or the cathode water surface at lower than 18.3 vol% during electrolysis so that mixed gas comprising the hydrogen gas and the diluent gas is supplied to a living organism, the mixed gas having a hydrogen gas concentration of 0.1 vol% or higher and lower than 18.3 vol%.
