Ignition plug and internal-combustion engine

An ignition plug comprising:

• an ignition plug body having a rod-shaped first conductive member, a cylindrical insulating material surrounding the first conductive member, and a cylindrical second conductive member having an eccentric penetration hole that houses therein the first conductive member and the insulating material, the cylindrical second conductive member having an earth electrode exposed to a combustion chamber so as to form a discharge gap between the earth electrode and the first conducting member, wherein an air-fuel mixture within the combustion chamber of an internal combustion engine is ignited when a potential difference is applied between the first conductive member and the cylindrical second conductive member, and electricity is discharged at the discharge gap;
• and
• an antenna attached to the ignition plug body that emits high-frequency EM radiation, which is externally provided, to the combustion chamber, wherein
• the antenna is located on a front-tip side surface of the cylindrical second conductive member and has two ends each reaching a vicinity of a base end of the earth electrode such that the antenna in its entire length extends along an outer circumferential edge of the cylindrical second conductive member, and
• a central axis of the eccentric penetration hole is shifted from a central axis of the cylindrical second conductive member.