Abstract: An ignition plug with a hollow cylindrical ground electrode, in which the center of a hollow cylindrical ground electrode is faced to the top of a center electrode, supported by a pair of stays, with a spark gap put in between so that the axial line of the center electrode and the axial line of a cylindrical hole of the ground electrode can fall on the same line and the sum of the center electrode's radius and the spark gap can be nearly equal to the radius of the cylindrical hole of the ground electrode. The model can be modified in various ways to increase the propagation speed of ignition and augment the power of expanding combustion gas.