A plasma jet plug has a cavity defined by a surface of a center electrode, an inner surface of an insulator, and a surface of a ground electrode. When a volume of a portion of the cavity on a front side of a front portion of the center electrode is a first volume V1 and a volume of a portion of the cavity on a rear side of the front end of the center electrode is a second volume V2, the following expression is satisfied: V1/V2≧0.20.