Glow plug and structure for mounting the same onto cylinder head including plug cap and cable

A glow plug is shortened and is standardized to be used for many kinds of the engines. A structure in which a glow plug having: an externally threaded portion 105 for mounting in a glow plug-mounting hole 11 in the engine head, a hexagonal portion for screwing, and an external connection terminal, is mounted in an internally threaded portion 15 in the mounting hole 11, wherein the external connection terminal is a pin terminal 109 that extends rearward in the axial direction, and the rear end of the pin terminal 109 is positioned within the hole 11. This makes connection with a wiring cord with a socket terminal simple, with no problems. The overall length of the glow plug can be set irrespective of the distance from the combustion chamber to the outer surface of the engine head, and can be standardized.