A gas sensor, comprising: a gas sensor element for detecting a specific gas component in gas under measurement, the gas sensor element including: a bottomed cylindrical base body formed of a solid electrolyte with a closed front end and an open rear end and extending in an axial direction of the gas sensor; an outer electrode formed of noble metal on an outer surface of the base body; and an inner electrode formed of noble metal on an inner surface of the base body; and a heater having a heating portion arranged in a cylindrical inner space of the base body, wherein the outer surface of the base body includes a gas contact region located on a front end side of the base body such that the gas under measurement comes into contact with the gas contact region; wherein the inner surface of the base body includes a gas contact inner region at a position located inside of the gas contact region in a thickness direction of the base body and a rear end region spaced apart from the gas contact inner region in the axial direction and located at a rear end side of the base body; wherein the heating portion has a heating resistor pattern located only in the same axial range as that where the gas contact inner region is located in the axial direction; wherein the inner electrode has: an inner sensing portion formed only in the gas contact inner region such that the inner sensing portion is located on at least the whole of a heat-facing area of the gas contact inner region that faces the heating resistor pattern in a radial direction of the base body; a terminal contact portion formed in the rear end region such that the terminal contact portion is located on at least a part of the rear end region in a circumferential direction of the base body; and a lead portion formed only on a part of the inner surface in the circumferential direction of the base body so as to connect the inner sensing portion and the terminal contact portion to each other; wherein the outer electrode has an outer sensing portion formed in the gas contact region such that a part of the outer sensing portion is located on at least a part of the gas contact region inside of which the inner sensing portion is located in the thickness direction of the base body; wherein a rear end of the inner sensing portion is located rear of a rear end of the outer sensing portion; and wherein the following condition: 1.1 ≤ T1/T2 is satisfied where T1 is a length between a front end of the gas sensor element and the rear end of the inner sensing portion in the axial direction; and T2 is a length between the front end of the gas sensor element and the rear end of the outer sensing portion in the axial direction; wherein a thickness of the outer sensing portion is larger than a thickness of the inner sensing portion. a gas sensor element for detecting a specific gas component in gas under measurement, the gas sensor element including: a bottomed cylindrical base body formed of a solid electrolyte with a closed front end and an open rear end and extending in an axial direction of the gas sensor; an outer electrode formed of noble metal on an outer surface of the base body; and an inner electrode formed of noble metal on an inner surface of the base body; and a heater having a heating portion arranged in a cylindrical inner space of the base body, wherein the outer surface of the base body includes a gas contact region located on a front end side of the base body such that the gas under measurement comes into contact with the gas contact region; wherein the inner surface of the base body includes a gas contact inner region at a position located inside of the gas contact region in a thickness direction of the base body and a rear end region spaced apart from the gas contact inner region in the axial direction and located at a rear end side of the base body; wherein the heating portion has a heating resistor pattern located only in the same axial range as that where the gas contact inner region is located in the axial direction; wherein the inner electrode has: an inner sensing portion formed only in the gas contact inner region such that the inner sensing portion is located on at least the whole of a heat-facing area of the gas contact inner region that faces the heating resistor pattern in a radial direction of the base body; a terminal contact portion formed in the rear end region such that the terminal contact portion is located on at least a part of the rear end region in a circumferential direction of the base body; and a lead portion formed only on a part of the inner surface in the circumferential direction of the base body so as to connect the inner sensing portion and the terminal contact portion to each other; wherein the outer electrode has an outer sensing portion formed in the gas contact region such that a part of the outer sensing portion is located on at least a part of the gas contact region inside of which the inner sensing portion is located in the thickness direction of the base body; wherein a rear end of the inner sensing portion is located rear of a rear end of the outer sensing portion; and wherein the following condition: 1.1 ≤ T1/T2 is satisfied where T1 is a length between a front end of the gas sensor element and the rear end of the inner sensing portion in the axial direction; and T2 is a length between the front end of the gas sensor element and the rear end of the outer sensing portion in the axial direction; wherein a thickness of the outer sensing portion is larger than a thickness of the inner sensing portion.