A temperature sensor comprising: a case including a body portion and a tubular portion projecting outward from the body portion , the tubular portion being formed in a tubular shape closed at a side defining a tip ; a temperature sensor element arranged within the tubular portion at the tip ; a wire member having one end connected to the temperature sensor element ; a holder to which the other end of the wire member is fixed; a substrate to which the other end of the wire member is electrically connected, the holder and the substrate being placed in the body portion ; a retaining portion disposed within the tubular portion at a position closer to the body portion than the temperature sensor element , the retaining portion being filled with a retaining material to support the wire member , wherein a gap between the holder , the substrate , and the body portion of the case is filled with the retaining material ; and a heat insulating section disposed between the temperature sensor element and the retaining portion , the heat insulating section including a heat insulating member made of a less heat-transferable material than the retaining material , wherein the heat insulating member in the heat insulating section is fixed around the wire member at a position near the temperature sensor element , wherein the temperature sensor element is pressed against the tip of the tubular portion , wherein the heat insulating member is made of foam polystyrene or a phenol resin, wherein the heat insulating section includes a gap portion filled with gas kept between the heat insulating member and the temperature sensor element , and wherein the retaining material is made of epoxy. a case including a body portion and a tubular portion projecting outward from the body portion , the tubular portion being formed in a tubular shape closed at a side defining a tip ; a temperature sensor element arranged within the tubular portion at the tip ; a wire member having one end connected to the temperature sensor element ; a holder to which the other end of the wire member is fixed; a substrate to which the other end of the wire member is electrically connected, the holder and the substrate being placed in the body portion ; a retaining portion disposed within the tubular portion at a position closer to the body portion than the temperature sensor element , the retaining portion being filled with a retaining material to support the wire member , wherein a gap between the holder , the substrate , and the body portion of the case is filled with the retaining material ; and a heat insulating section disposed between the temperature sensor element and the retaining portion , the heat insulating section including a heat insulating member made of a less heat-transferable material than the retaining material , wherein the heat insulating member in the heat insulating section is fixed around the wire member at a position near the temperature sensor element , wherein the temperature sensor element is pressed against the tip of the tubular portion , wherein the heat insulating member is made of foam polystyrene or a phenol resin, wherein the heat insulating section includes a gap portion filled with gas kept between the heat insulating member and the temperature sensor element , and wherein the retaining material is made of epoxy. <EOS>