PURPOSE: To obtain the titled combined form by engaging the projected part of a ceramic member and the recessed part of a metallic member by specified method to reduce the stress concentration to be developed in said ceramic member due to flexural loading thus leading to enhancing the strength of the form as a whole.

CONSTITUTION: The objective form can be obtained by integrally combining the projected part of a ceramic member and the recessed part 3 of a metallic member in such a manner that an engagement is performed so as to provide a gap l1 larger than the diameter l2 of the smaller diameter part 4 of the ceramic member 1 between the shoulder 6 of the larger diameter part of said member 1 and the lower end 5 of the metallic member 2 followed by processing so as to gradually reduce the wall thickness of the end 7 of the member 2 with a radius of curvature R of ≥0.4 times the diameter l2 towards the member 1 to the effect that the length l4 of the wall thickness-reducing part and the tip wall thickness l3 be, respectively, ≥0.5 times and ≤0.2 times the diameter l2.