To enhance treatment effects by means of an antioxidative action by arbitrarily setting the density of hydrogen gas to be inhaled.

To a hydrogen gas generator 1, an electrolysis current value control unit 25 for controlling electrolysis current value is fitted. An air mixer 14 is installed to a part of a conduit leading the hydrogen gas generated by the hydrogen gas generator 1 to a nasal cavity canula 3 to mix the air and the hydrogen gas sent from an air pump 15 with the mixer 14, so that the hydrogen gas whose density is adjusted is sent to the side of the nasal cavity canula 3. A hydrogen gas density detection sensor 17 is provided between the mixer 14 and the nasal cavity canula 3 and according to the density of the hydrogen gas detected by the hydrogen gas density detection sensor 17, feedback control is performed to current value applied to the hydrogen gas generator 1 by using the electrolysis current value control unit 25.