A gas concentration detection sensor , comprising: a sensor element that detects concentration of a selected gas included in an object gas; a first protection cover that covers over the sensor element and has a first gas introduction aperture arranged around a stem section of the first protection cover allowing for a flow of the object gas from outside to inside of the first protection cover; a second protection cover that covers over the first protection cover and has a second gas introduction aperture allowing for a flow of the object gas from outside to inside of the second protection cover; and a gas flow path that runs from the second gas introduction aperture through a space between the first protection cover and the second protection cover to the first gas introduction aperture , enters inside of the first protection cover via the first gas introduction aperture, and reaches a free end of the sensor element ; and a ring-shaped inner wall member is attached to an outer circumferential face of said stem section of the first protection cover , the ring-shaped inner wall member being of a solid form arranged to at least partially narrow the width (W) of a flow path from the second gas introduction aperture to the first gas introduction aperture in the gas flow path and located in the periphery of the free end of the sensor element, wherein said width (W) of said flow path between an inner circumferential face of the second protection cover and an outer circumferential face of said ring-shaped inner wall member is in the range 0.1-1.5 mm, characterized in that : a length (L) of said flow path between said inner circumferential face of the second protection cover and said outer circumferential face of said ring-shaped inner wall member is in the range 1-5 mm. a sensor element that detects concentration of a selected gas included in an object gas; a first protection cover that covers over the sensor element and has a first gas introduction aperture arranged around a stem section of the first protection cover allowing for a flow of the object gas from outside to inside of the first protection cover; a second protection cover that covers over the first protection cover and has a second gas introduction aperture allowing for a flow of the object gas from outside to inside of the second protection cover; and a gas flow path that runs from the second gas introduction aperture through a space between the first protection cover and the second protection cover to the first gas introduction aperture , enters inside of the first protection cover via the first gas introduction aperture, and reaches a free end of the sensor element ; and a ring-shaped inner wall member is attached to an outer circumferential face of said stem section of the first protection cover , the ring-shaped inner wall member being of a solid form arranged to at least partially narrow the width (W) of a flow path from the second gas introduction aperture to the first gas introduction aperture in the gas flow path and located in the periphery of the free end of the sensor element, wherein said width (W) of said flow path between an inner circumferential face of the second protection cover and an outer circumferential face of said ring-shaped inner wall member is in the range 0.1-1.5 mm, <EOS>