In a temperature sensor, two seal members seal the open opposite ends of a cladding member (a forward end and a rear end), so that water absorption by an insulator of a sheath member can be restrained. The seal members are formed to have an insulation resistance equal to that of a conductor-fixing material. Therefore, even when the temperature sensor is used in a high-temperature environment, the insulation performance of the seal members does not become lower than the insulation performance of the conductor-fixing material, so that the formation of a leakage current path can be suppressed. According to the temperature sensor, the electrical property of a temperature sensitive element can be sensed accurately, and a reduction in the accuracy of temperature sensing can be restrained.