PURPOSE: To mount/dismount a primary radiator to/from a rear side of an antenna reflecting mirror by using a straight line close to a center line of a radiation section as a rotary axis and turning a metallic plate around the axis.

CONSTITUTION: A metallic plate 3 having a similar shape to that of a bent waveguide 2 being a feeder is turned around a center line of a radiation section 2, that is, around an antenna center shaft with a turning shaft 4. The metallic plate 3 is turned and moved in this state, a tip of the primary radiator is protruded toward a front face through a hole whose diameter is small in the center from a rear side of an antenna reflecting mirror 6 and the primary radiator is fitted to the antenna reflecting mirror 6. Then the turning shaft 4 is turned to move the metallic plate 3 to a position symmetrical to the bent waveguide 2 with respect to the antenna center axis and fixed by a fixing screw 5. Moreover, a radio wave absorbing body is provided to the metallic plate 3, at need, to reduce a side lobe.