An endodontic instrument for root canal filling includes a body having DC power source and printed circuit board, a heating tip connected to the body, a switch, and a control circuit for switching on/off power supply to the heating tip. The heating tip includes a first metal part serving as a resistant tube, a second metal part disposed inside the first metal part and configured to supply power, check a thermoelectric power (+) terminal, a third metal part disposed inside the first metal part and configured to supply power, a contact part, an insulator disposed inside the first metal part and enclosing surfaces of the second and third metal parts, first conductive tube, a second conductive tube; and an insulator connected and fixed to the first and second conductive tubes, where temperature is detected using thermoelectric power of the thermocouple.