An insulator (2) is inserted into a metallic shell (1) in the direction
of an axis O, and a sealing material powder (160) is charged into a circumferential
gap (20) formed between the inner circumferential surface of a rear end
portion of the metallic shell (1) and the outer circumferential surface
of the insulator (2). The compressed sealing-material-powder layer (61)
contains talc in an amount of from 75% to 99.7% by mass and at least one of magnesite
and dolomite in an amount of from 0.3% to 25% by mass, and satisfies 0.5M1.3
and 0.5L2(M4.5), wherein L in mm represents height
as measured in the direction of the axis O, and M in mm represents thickness as
measured radially with respect to the axis O.
