Gas sensor

A gas sensor, comprising:

• a cylindrical metal shell arranged in an axial direction of the gas sensor;
• a holder placed in the metal shell and formed with an axial through hole;
• and
• an elongated plate-shaped or rod-shaped sensor element inserted through the axial through hole of the holder with a front end of the sensor element protruding toward the front from a front end face of the holder, the sensor element having, at a front end part thereof, a detection portion covered with a porous protection layer, the porous protection layer being formed on a predetermine region from the front end of the sensor element toward the rear and having a rear end located on or at a front side with respect to a front end of the axial through hole of the holder,
• wherein the holder has a recessed portion formed in a region enclosing the axial through hole when viewed from the front end face of the holder;
• wherein the recessed portion is recessed toward the rear from the front end face of the holder;
• and
• wherein the sensor element passes through the recessed portion such that the rear end of the porous protection layer is situated within the recessed portion of the holder and is located at a rear side with respect to the front end face of the holder while maintaining a space between an inner circumferential surface of the recessed portion and an outer circumferential surface of the porous protection layer.