A high concentration hydrogen gas supply device for living bodies includes: an electrolytic bath (1) which includes an electrolytic chamber (11) to which raw water to be electrolyzed (12) is introduced at least one partition (13) that divides the electrolytic chamber into the inside and the outside and at least one pair of electrode plates (14, 15) provided respectively for the inside and the outside of the electrolytic chamber and sandwiching the partition and in which the electrode plate located in the outside of the electrolytic chamber makes contact with the partition； a direct current power supply (2) for applying a direct current voltage to the pair of the electrode plates； and a diluent gas supplier (3) for diluting hydrogen gas generated from the electrode plate serving as the cathode. The hydrogen gas supply device makes the diluent gas supplied from the diluent gas supplier flow to the cathode to supply mixed gas that includes the hydrogen gas and the diluent gas and that has a hydrogen gas concentration of 0.1 to 18.3 vol% to a living body while maintaining the hydrogen gas concentration in the vicinity of the cathode during electrolysis always at lower than 18.3 vol%.
