A plug cap comprising: an electrical connection portion for electrically connecting a spark plug to a plug cord, the spark plug being connectable to one end of the electrical connection portion and the plug cord being connectable to the other end of the electrical connection portion; a terminal body that is made of a resin, is provided on an outer periphery of the electrical connection portion, and includes a one end-side insertion portion which is formed at one end of the terminal body and into which the spark plug is inserted and the other end-side insertion portion which is formed at the other end of the terminal body and into which the plug cord is inserted, at least the one end-side insertion portion and the other end-side insertion portion being formed in a cylindrical shape; and a cylindrical rubber member which is mounted on at least one of one end portion and the other end portion of the terminal body and into which the spark plug or the plug cord is inserted, wherein the rubber member includes a cylindrical inner cylindrical portion that is inserted into the one end-side insertion portion or the other end-side insertion portion of the terminal body, a cylindrical outer cylindrical portion that is positioned close to the outer periphery of the inner cylindrical portion and is disposed with the terminal body interposed between the outer cylindrical portion and the inner cylindrical portion, and a connecting portion that connects the outer cylindrical portion to the inner cylindrical portion, and characterised in that the inner cylindrical portion includes an annular protrusion that comes into contact with the inner peripheral surface of the terminal body. an electrical connection portion for electrically connecting a spark plug to a plug cord, the spark plug being connectable to one end of the electrical connection portion and the plug cord being connectable to the other end of the electrical connection portion; a terminal body that is made of a resin, is provided on an outer periphery of the electrical connection portion, and includes a one end-side insertion portion which is formed at one end of the terminal body and into which the spark plug is inserted and the other end-side insertion portion which is formed at the other end of the terminal body and into which the plug cord is inserted, at least the one end-side insertion portion and the other end-side insertion portion being formed in a cylindrical shape; and a cylindrical rubber member which is mounted on at least one of one end portion and the other end portion of the terminal body and into which the spark plug or the plug cord is inserted, wherein the rubber member includes a cylindrical inner cylindrical portion that is inserted into the one end-side insertion portion or the other end-side insertion portion of the terminal body, a cylindrical outer cylindrical portion that is positioned close to the outer periphery of the inner cylindrical portion and is disposed with the terminal body interposed between the outer cylindrical portion and the inner cylindrical portion, and a connecting portion that connects the outer cylindrical portion to the inner cylindrical portion, and characterised in that the inner cylindrical portion includes an annular protrusion that comes into contact with the inner peripheral surface of the terminal body.