PURPOSE: To easily alloy an omnidirectional antenna to have directively, and to interrupt a useless radio wave by providing an opening in the fixed direction of a cylindrical main body constituted of conductive materials around the omnidirectional antenna.

CONSTITUTION: A cylindrical main body 3 formed of the conductive materials is provided around an omnidirectional antenna 2 erected perpendicularly to the upper face of a communication equipment 1. The main body 3 is equipped with an opening 4 at one part, the upper part of the antenna 2 is covered with an upper wall 3a, and the main body 3 is fixed to an interfitting groove 1a of the upper face of the communication equipment 1 so as to be rotatable. Thus, when the main body 3 is rotated, and the opening 4 is faced to a directly reaching wave, the directly reaching wave is transmitted through the opening 4 to the antenna 2. However, the most of a reflected wave is shielded by the main body 3, and it is not transmitted to the antenna 3. Therefore, a multi-path state can be avoided.