A gas sensor including a plate-shaped detecting element is disclosed, wherein the detecting element has a pair of principle surfaces and a pair of side surfaces adjacent to the pair of principle surfaces, in a radical direction thereof, wherein a first chamfered portion is provided between at least one first principal surface of the pair of principal surfaces and the rear end surface of the detecting element, and wherein the angle between a first axis ridgeline portion formed by the first principal surface and a first side surface that is one of the pair of side surfaces and extending in the direction of the axis, and a first width ridgeline formed by the first principal surface and the first chamfered portion and extending in a width direction is larger than 90°.