A gas sensor adapted for disposing in an intake passage of an internal combustion engine, which comprises: a detecting element extending in an axial direction and comprising a detecting portion for detecting a specific gas component in a gas to be measured on a leading end side of the gas sensor; and a protector having a tube portion surrounding the detecting portion from outside in a radial direction and a bottom portion connected to a leading end side of the tube portion, the protector having a first opening which is disposed at the tube portion so as to face the downstream side of the intake passage in the internal combustion engine, and which allows the gas to be measured to flow into the tube portion, and a second opening at the bottom portion through which the gas to be measured flows, and wherein the bottom portion includes a first bottom wall portion and a second bottom wall portion, the second bottom wall portion protrudes toward the leading end side in the axial direction, and at least a part of an inner face of the second bottom wall portion is located at the leading end side in the axial direction with respect to an outer face of the first bottom wall portion, the second opening facing the downstream side of the intake passage is provided on a side opposite the inner space of the tube portion in a communication passage formed by the inner face of the second bottom wall portion, the communication passage is formed so that an opening area of the second opening is larger than an area of a largest imaginary circle that can be placed inside the first opening when the first opening is viewed planarly in a direction perpendicular to the central axis of the tube portion, when viewed from an upstream side of the intake passage, the second opening is blocked by an outer face of the second bottom wall portion, and wherein the first and second openings are visible when the gas sensor is disposed in the intake passage, and the gas sensor is viewed from the downstream side of the intake passage, and wherein the protector is adapted so that a majority of a gas to be measured flowing through the inside of the protector is introduced to the inside of the protector through the first opening, and released to the outside of the protector through the communication passage and the second opening. a detecting element extending in an axial direction and comprising a detecting portion for detecting a specific gas component in a gas to be measured on a leading end side of the gas sensor; and a protector having a tube portion surrounding the detecting portion from outside in a radial direction and a bottom portion connected to a leading end side of the tube portion, the protector having a first opening which is disposed at the tube portion so as to face the downstream side of the intake passage in the internal combustion engine, and which allows the gas to be measured to flow into the tube portion, and a second opening at the bottom portion through which the gas to be measured flows, and wherein the bottom portion includes a first bottom wall portion and a second bottom wall portion, the second bottom wall portion protrudes toward the leading end side in the axial direction, and at least a part of an inner face of the second bottom wall portion is located at the leading end side in the axial direction with respect to an outer face of the first bottom wall portion, the second opening facing the downstream side of the intake passage is provided on a side opposite the inner space of the tube portion in a communication passage formed by the inner face of the second bottom wall portion, the communication passage is formed so that an opening area of the second opening is larger than an area of a largest imaginary circle that can be placed inside the first opening when the first opening is viewed planarly in a direction perpendicular to the central axis of the tube portion, when viewed from an upstream side of the intake passage, the second opening is blocked by an outer face of the second bottom wall portion, and wherein the first and second openings are visible when the gas sensor is disposed in the intake passage, and the gas sensor is viewed from the downstream side of the intake passage, and wherein the protector is adapted so that a majority of a gas to be measured flowing through the inside of the protector is introduced to the inside of the protector through the first opening, and released to the outside of the protector through the communication passage and the second opening.