Gas sensor

A gas sensor comprising:

• a sensor element extending in an axial-line direction and having a detection portion on a front-end side thereof;
• a tubular casing inside which the sensor element is placed, the casing having an opening at a rear end thereof;
• a lead wire electrically connected to the sensor element and extending outside the gas sensor through the opening;
• and
• an elastic member having a terminal passage hole through which the lead wire passes, the terminal passage hole having two or more annular projecting ridges on an inner surface thereof, the elastic member being placed on a rear-end inner side of the casing and sealing the opening, wherein
• the casing is reduced in diameter by a crimping portion on an outer side of the projecting ridges so that the projecting ridges contact with an outer surface of the lead wire in an airtight state, and
• when the elastic member is viewed in a state of being removed from the casing, an inner diameter of a first projecting ridge which is the projecting ridge on a most-front-end side is smallest among inner diameters of all the projecting ridges.