A thermistor of which resistance is changed depending on temperature and a secondary battery to which the thermistor is attached are disclosed. The thermistor is attached to an object via a lead which is made of different kinds of materials. The lead is configured so that a part of the lead to be united to the thermistor electrode is mainly made of the same material as the electrode and a part of the lead to be united to the object is mainly made of the same material as the surface of the object. Thus, the thermistor may be simply attached to the object only using the ultrasonic welding, thereby remarkably reducing junction inferiorities.