Spark plug for internal combustion engines and internal combustion engine

A spark plug, having a tip end in an axial direction thereof, for an internal combustion engine , comprising:

• a tubular housing;
• a tubular insulator that has a tip and that is retained inside the housing;
• a central electrode that has an end portion and that is retained inside the insulator, the end portion of the central electrode being exposed from the tip of the insulator toward the tip end of the spark plug;
• and
• a ground electrode that enables a discharge to be generated between the ground electrode and the central electrode,
• wherein
• the spark plug has a specific direction that is orthogonal to the axial direction of the spark plug;
• the specific direction has opposing first and second sides, the first and second sides being respectively defined as a front directional side and a rear directional side;
• the housing has a tip surface that has a front end in the front side of the specific direction and a rear end in the rear side of the specific direction, the tip surface having a tip inclined surface that is inclined toward the tip end of the spark plug from the front end to the rear end of the tip surface;
• and
• the tip inclined surface has a front end and a rear end in the specific direction, the insulator having a front end in the front side of the specific direction, the rear end of the tip inclined surface being located to be closer to the tip end of the spark plug than the front end of the tip surface is, and being located to be more rearward than the front end of the insulator in the rear side of the specific direction, the tip inclined surface having a length between the front end and the rear end, the insulator and the housing having a gap formed between the outer circumferential surface of the insulator and the end portion of the inner circumferential surface of the housing, the length between the front end and the rear end being longer than the gap.