An apparatus includes an electrolytic cell having an electrolytic chamber to which subject raw water is introduced, at least one membrane that separates inside and outside of the electrolytic chamber, and at least one pair of electrode plates 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 that applies a direct-current voltage to the pair of electrode plates; and a diluent gas supplier for diluting hydrogen gas generated from the electrode plate that is to be a cathode, wherein the apparatus blows diluent gas supplied from the diluent gas supplier to the cathode thereby to constantly maintain a hydrogen gas concentration in the vicinity of the cathode during electrolysis at lower than 18.3 vol % so that mixed gas comprising the hydrogen gas and the diluent gas and having a hydrogen gas concentration of 0.1 to 18.3 vol % is supplied to a living organism.