Abstract: The vane 1 is substantially in a flat rectangular parallelepiped shape having (a) two wide side surfaces 1c, 1c′ opposing in the thickness direction and being slidable in each guide groove 12 of a rotor 11 of an actuator, (b) two narrow side surfaces 1d, 1d′ opposing in the width direction, (c) an as-cold-worked top surface 1a having an arcuately projecting cross section in a plane perpendicular to the width direction and being in slidable contact with a cam surface 14 of the actuator 13 for sealing, and (d) a bottom end surface 1e opposing the top surface 1a, both ends of said top surface 1a in the width direction being bulging toward the cam surface 14.