A small diameter section (4a) formed at the rear end of a ceramic heater (4) fixed in a metallic outer tube (8) is prevented from being damaged. The ceramic heater (4) is fixed in the metallic outer tube (8) by brazing etc. with a heat producing section at the head exposed to the outside. The rear end of the ceramic heater (4) is positioned inside the metallic outer tube (8), and at the rear end is formed a small diameter section (4b). The rear end small diameter section (4b) of the ceramic heater (4) is connected to an electrode lead-out member (electrode lead-out wire (10)) for taking out the positive electrode of a heat producing body. Granulated powder (alumina, for example)(18) of an inorganic insulating material is filled in around the connection section, in the metallic outer tube (8), of the ceramic heater (4) and the electrode lead-out wire (10), and in addition, magnesia (20) is sealed outside the granulated powder. After that, swaging is performed to bring the magnesia (20)into a highly dense state, fixing the electrode lead-out wire (10) and an electrode lead-out rod (12) in the metallic outer tube (8).