It is significant to manufacture a constant temperature type fire alarm detector operated by a lower power, as green technology. Constant temperature type fire detectors may be operated by a method using a bimetal or a method using a thermistor. According to the constant temperature type fire detector using the bimetal, aluminum may be oxidized at a contact point of the bimetal, so that it may not be operated at a predetermined set temperature. Additionally, an aluminum plate may have high cost. The constant temperature type fire detector using the thermistor may use three or more grounds, so that a stand by current may be great. Additionally, the constant temperature type fire detector using the thermistor may include ten parts for detecting a constant temperature, so that manufacture cost may increase. Furthermore, when the constant temperature type fire detector using the thermistor is operated for a long time, trouble rates of the parts may increase and durability of the parts may be deteriorated. Thus, alternative methods for solving the above problems have been required for a long time.