Spark plug that prevents gas turbulence in the discharge space

A spark plug comprising a metal shell having a cylindrical shape, a center electrode disposed in an inside of the metal shell and a ground electrode connected to the metal shell, and having a curved shape arranged facing a distal end surface of the central electrode, a virtual plane along the curved shape of the ground electrode facing a flow of a fuel mixture gas, the ground electrode comprising a base part, wherein

• the base part of the ground electrode comprises:
• a facing surface formed on an upper surface of the base part at a position facing the distal end surface of the central electrode to form a spark gap between the facing surface and the distal end surface of the central electrode;
• a first slope surface formed on the upper surface of the base part and connected to the facing surface, and increasingly away from the distal end surface of the central electrode in a flow direction of the fuel mixture gas,
• a downstream-side end surface formed at a most downstream side in the flow direction of the fuel mixture gas and parallel with the virtual plane, and connected to the first slope surface;
• a second slope surface formed on a lower surface of the base part and connected to the downstream-side end surface, and
• approaching the distal end surface of the central electrode in the flow direction of the fuel mixture gas;
• and
• an opposing surface formed on the lower surface of the base part, and farthest away from the distal end surface of the central electrode,
• wherein a width A1 of the facing surface of the base part is wider than a width A2 of the opposing surface of the base part,
• a first angle θ1 of the facing surface to the first slope surface satisfies a relationship of 10°θ1≤40°, and
• a first distance L1 satisfies a relationship of 0.3 mm≤L1≤0.9 mm, where the first distance is measured, in the central axis of the central electrode to which the central electrode is disposed into the metal shell, from a connection point between the second slope surface and the downstream-side end surface to the facing surface of the base part.