PURPOSE: To eliminate a backlash at the time of shipping caused by a space between an antenna rotation section and a rotation support section by using a movable spacer to be inserted between a rotation section and a rotation support section.

CONSTITUTION: An outside surface (c) of a fixed block 11 comes into contact with the surface of the antenna rotation section. The outside surface of a movable block 12 presses the surface of the rotation support section. When a press bolt 13 is rotated in one direction, a movable block 12 slides along a guide groove 17 upwards the movable direction S. Thus, the length G between both blocks is shifted to the expanding direction to come into contact with the surface of the rotation support section. Then, when the press bolt 13 is rotated in the opposite direction, the movable block 12 slides along the guide groove 17 downward the movable direction S, to be shifted in the direction making the length G shorter. Moreover, a sphere end 16 of the press bolt 13 rotates the press bolt 13, making a slide while maintaining a certain degree of engagement.