A continuous measurement method for hydrogen gas concentration, the method comprising: a step of placing a hydrogen gas permeable material in such a manner as to come in contact with a flowing hydrogen water containing hydrogen gas and introducing, from the hydrogen water, a hydrogen gas passing through the hydrogen gas permeable material into a hollow part ; a step of introducing a first gas substantially inert to hydrogen into the hollow part through a gas supply pump provided on a gas supply conduit connected to the hollow part and extracting and exhausting a hydrogen gas-containing gas as a second gas in an amount equal to that of the first gas, from the hollow part through a gas exhaust pump provided on a gas exhaust conduit connected to the hollow part ; a step of circulating the hydrogen gas that has passed through the hydrogen gas permeable material and has been introduced into the hollow part from the hydrogen water, through the gas supply conduit into the hollow part by a circulation pump provided on a circulation conduit that is branched from the gas exhaust conduit and is connected to the gas supply conduit ; a step of measuring a hydrogen gas concentration in the hollow part when an equilibrium state between a concentration of hydrogen gas contained in the hydrogen water and a concentration of hydrogen gas introduced into the hollow part is achieved; and a step of previously determining a relation between a concentration of hydrogen gas contained in the hydrogen water and a concentration of hydrogen gas introduced into the hollow part and, based on said relation, calculating a concentration of hydrogen gas contained in the hydrogen water from the measured hydrogen gas concentration, wherein said step of measuring the hydrogen gas concentration is carried out at an upstream side from the gas exhaust pump on the gas exhaust conduit . a step of placing a hydrogen gas permeable material in such a manner as to come in contact with a flowing hydrogen water containing hydrogen gas and introducing, from the hydrogen water, a hydrogen gas passing through the hydrogen gas permeable material into a hollow part ; a step of introducing a first gas substantially inert to hydrogen into the hollow part through a gas supply pump provided on a gas supply conduit connected to the hollow part and extracting and exhausting a hydrogen gas-containing gas as a second gas in an amount equal to that of the first gas, from the hollow part through a gas exhaust pump provided on a gas exhaust conduit connected to the hollow part ; a step of circulating the hydrogen gas that has passed through the hydrogen gas permeable material and has been introduced into the hollow part from the hydrogen water, through the gas supply conduit into the hollow part by a circulation pump provided on a circulation conduit that is branched from the gas exhaust conduit and is connected to the gas supply conduit ; a step of measuring a hydrogen gas concentration in the hollow part when an equilibrium state between a concentration of hydrogen gas contained in the hydrogen water and a concentration of hydrogen gas introduced into the hollow part is achieved; and a step of previously determining a relation between a concentration of hydrogen gas contained in the hydrogen water and a concentration of hydrogen gas introduced into the hollow part and, based on said relation, calculating a concentration of hydrogen gas contained in the hydrogen water from the measured hydrogen gas concentration, wherein said step of measuring the hydrogen gas concentration is carried out at an upstream side from the gas exhaust pump on the gas exhaust conduit . <EOS>