A gas concentration detection sensor, comprising: a sensor element that is held with a housing with a front end thereof exposed and is able to detect a concentration of a specified gas included in an object gas; a protective cover that is secured to the housing and protects the front end of the sensor element, and an inner cover that is one of components of the protective cover and covers the front end of the sensor element, the inner cover having an inner gas aperture that allows the object gas to flow therethrough; and an outer cover that is one of the components of the protective cover and covers the inner cover, the outer cover having an outer gas aperture that allows the object gas to flow therethrough, the outer gas aperture not opposing the inner gas aperture, wherein a ratio φ1/φ2 is from 0.6 to 0.9 where φ1 represents an outer diameter of a portion where the inner gas aperture is formed in the inner cover, and φ2 represents an inner diameter of a portion where the outer gas aperture is formed in the outer cover; the inner cover includes: a first body where the inner gas aperture is formed, a second body that is connected to the first body with a step provided therebetween, the second body having a diameter smaller than a diameter of the first body, and a front end section that is connected to the second body, the front end section having a reverse truncated triangular pyramid shape; and the outer cover includes a body where the outer gas aperture is formed, and a front end section that is connected to the body with a step provided there between, the front end section and the second body of the inner cover being joined circumferentially such that a space defined by the inner cover and the outer cover is divided into an upper chamber and a lower chamber, the front end section having a diameter smaller than a diameter of the body. a sensor element that is held with a housing with a front end thereof exposed and is able to detect a concentration of a specified gas included in an object gas; a protective cover that is secured to the housing and protects the front end of the sensor element, and an inner cover that is one of components of the protective cover and covers the front end of the sensor element, the inner cover having an inner gas aperture that allows the object gas to flow therethrough; and an outer cover that is one of the components of the protective cover and covers the inner cover, the outer cover having an outer gas aperture that allows the object gas to flow therethrough, the outer gas aperture not opposing the inner gas aperture, wherein a ratio φ1/φ2 is from 0.6 to 0.9 where φ1 represents an outer diameter of a portion where the inner gas aperture is formed in the inner cover, and φ2 represents an inner diameter of a portion where the outer gas aperture is formed in the outer cover; the inner cover includes: a first body where the inner gas aperture is formed, a second body that is connected to the first body with a step provided therebetween, the second body having a diameter smaller than a diameter of the first body, and a front end section that is connected to the second body, the front end section having a reverse truncated triangular pyramid shape; a first body where the inner gas aperture is formed, a second body that is connected to the first body with a step provided therebetween, the second body having a diameter smaller than a diameter of the first body, and a front end section that is connected to the second body, the front end section having a reverse truncated triangular pyramid shape; and the outer cover includes a body where the outer gas aperture is formed, and a front end section that is connected to the body with a step provided there between, the front end section and the second body of the inner cover being joined circumferentially such that a space defined by the inner cover and the outer cover is divided into an upper chamber and a lower chamber, the front end section having a diameter smaller than a diameter of the body.