Each of the flat surfaces of the pin-seal portions is formed such that the width thereof in the second direction gradually increases as far as the portion upper than the stud pin in the direction from the side of the face portion to the side of the seal end surface, and forms the symmetrical shape about the center portion in the second direction. Namely, the flat surface is formed so as to have the substantially half ellipse shape which has the major axis in the second direction, and protrudes toward the face portion.
