Abstract: A spark plug that provides an increase in the combustion speed of an engine. The spark plug includes a center electrode, a ground electrode, an insulator, and a cover portion. In a cross-sectional area of a region surrounded by an inner wall surface of the cover portion in a cross section taken along a plane perpendicular to an axial line CX of the spark plug, the cover portion includes: a narrow portion positioned on the front end side with respect to the ground electrode in the direction of the axial line CX and narrowed such that the cross-sectional area is smallest; and a cover front portion positioned on the front end side of the narrow portion and having the cross-sectional area that is larger than the cross-sectional area of the narrow portion and that is largest at the front end of the cover front portion.

Abstract: A back electrode (6), linear hot cathodes (7) as electron beam sources, and an electrode unit (8) are placed on and fixed to a rear case (4). On the other hand, wire electrodes (9) fixed to a grid frame (10) are positioned relative to stripes of a phosphor screen (2) and are then placed on and fixed to a supporting frame (11) placed in a front case (3) using stud pins (21). According to such a configuration, when the front case and the rear case are bonded and are thus fixed, the position shift between the phosphor screen (2) and the wire electrodes (9) can be suppressed within a tolerance. As a result, a flat-type display apparatus that can display excellent images can be provided.