ceramic plate 5c the upper insulator 4a and the lower insulator 4b are made of thermally and electrically insulating material such as phenol resin to the upper insulator 4a and the lower insulator 4b the positive electrode plate 6 and the negative electrode plate 7 are molded respectively the insulators 4a 4b are joined to each other by bolts 9 while an 0 ring 8 is interposed therebetween the positive electrode plate 6 and the negative electrode plate 7 are made of a copper plate plated with nickel respectively as shown in fig2 the positive electrode plate 6 is in contact with the outer peripheral portion of the upper surface of the ceramic plate 5a the positive electrode plate 6 is connected to a battery 11 through a key switch 10 as shown in fig1 the negative electrode 7 is in contact with the outer peripheral portion of the under surface of the ceramic plate 5c and is grounded hereinafter the structure of the ceramic heater a will be explained in detail each of the ceramic plates 5a 5b 5c is made of ptc ceramic containing barium titanate as a main ingredient as shown in fig2 and 3 each ceramic plate is formed into a circular plate of which the diameter is about 40 mm and the thickness is about 2 mm and seven open holes 50 are formed in the center of the circular plate and in the outer peripheral portion thereof at equal distances on the upper surface of each of the ceramic plates 5a 5b 5c except a horseshoe shaped portion 55 which extends along the outer periphery thereof each of the electrode surfaces 51a 51b 51c is formed one portion of.