In a hydrogen concentration measurement device that employs a proton conducting electrolyte membrane, more stable measurement of hydrogen concentration that is less susceptible to temperature and humidity state of measurement target gas becomes possible. [...

A hydrogen sensor includes a first electrode 3 and a second electrode 4 provided in contact with a proton conduction layer 2; a gas diffusion controlling portion 6 provided between a measurement gas atmosphere and the first electrode 3; and a support eleme...