Spark plug of internal combustion engine

A spark plug comprising:

• a spark plug housing having a cylindrical shape;
• an insulator having a cylindrical shape and being arranged in and supported by an inside of the spark plug housing;
• a central electrode supported in an inside of the insulator, and a front end part of the central electrode projecting;
• a ground electrode being arranged to form a discharge gap between the central electrode and the ground electrode,
• the ground electrode comprising a rod-shaped part and an opposing part, the rod-shaped part extending from a front end part of the spark plug housing toward a front end part of the spark plug, the opposing part having a curved shape which being curved from the rod-shaped part inwardly in a radius direction of the spark plug, and the opposing part facing the central electrode,
• the opposing part comprising a flat surface part and a slope surface part, the flat surface part having a flat-shaped surface which faces the central electrode side, the slope surface part being formed on a part of the opposing part along an extending direction of the opposing part, the opposing part being gradually separated from the central electrode along a width direction of the opposing part,
• wherein the spark plug has a ratio V/W within a range of 0.5<V/W<2.0, where V indicates a length of the opposing part measured in a gap formation direction in which the central electrode, the discharge gap and the opposing part are arranged in order, and W indicates a width length of the opposing part in the width direction of the opposing part,
• the slope surface part has a first end part and a second end part, the first end part of the slope surface part is connected to an end part of the flat surface part in the width direction of the opposing part, and
• the second end part of the slope surface part is connected to an end part of a back surface of the opposing part, and the back surface of the opposing part is opposite to a front surface of the opposing part, and the opposing part faces the central electrode side in the gap formation direction.