| 摘要 |
To sufficiently increase the density of a resistor for realizing excellent load life performance in a spark plug in which difficulty is encountered in increasing the density of the resistor. A spark plug 1 includes a center electrode 5; a terminal electrode 6; and a resistor 7 provided between the electrodes 5 and 6, and containing a glass containing SiO 2 and B 2 O 5 . The distance between the forward end of the terminal electrode 6 and the rear end of the center electrode 5 is 15 mm or more, and the glass is a phase-separated glass having aggregate phase 41 and an intervening phase 42. In a cross section of the resistor 7 having a width of 1.3 mm, when a plurality of imaginary lines perpendicular to an axial line CL1 are drawn at intervals of 0.1 mm in the direction of the axial line CL1, the number of aggregate phase 41 located on each of the imaginary lines is determined, and the average number of aggregate phase per imaginary line is determined for each of a plurality of line groups each consisting of five consecutive imaginary lines, there are three or more consecutive line groups which satisfy the condition that the average number of aggregate phase per imaginary line is larger, by 5 or more, than the minimum average number of aggregate phase per imaginary line among the plurality of line groups. |
