Temperature sensor with quick response

A temperature sensor comprising:

• a cylindrical metal tube extending in an axial direction and having a front end portion including a sidewall and a closed bottom;
• a thermal sensing element held in an inside of said metal tube and including a thermal sensing portion with electrical characteristic varying according to a temperature, and a pair of electrode wires provided in said thermal sensing portion and extending toward a rear end portion of said metal tube;
• and
• a sheath member held in an inside of said metal tube and including a sheath pipe in which a pair of metal cores connected to said pair of electrode wires of said thermal sensing element are held while electrically insulated, wherein:
• said metal tube has a small-diameter portion located on said front end portion and entirely having an inner diameter smaller than an outer diameter of said sheath member, and a large-diameter portion located on a rear end portion of said small-diameter portion and having a diameter larger than an outer diameter of said small-diameter portion;
• and
• said thermal sensing portion is held in said small-diameter portion and an electrically insulating member is filled at least in between a front end of said thermal sensing portion and an inner wall of the closed bottom of said metal tube.