PURPOSE: To obtain an excellent VSWR characteristic to each polarized wave after branching over a wide band by forming a prescribed conductor part to an aperture formed to the side face of a main waveguide at a right angle to a 1st polarized wave and in parallel with a 2nd polarized wave.

CONSTITUTION: The aperture 16 of the same shape of the aperture of a waveguide 13 is formed to a bonded part between a main waveguide 11 and a branch waveguide 13. Then three conductor rods 17a∼17c are provided on the aperture 16 at a prescribed interval in parallel with its long side, that is, at a right angle to a polarized wave (a) and in parallel with a polarized wave (b). Through the constitution above, since the conductor rods 17a∼17c are in parallel with the polarizer wave (b), the waveguide is in short-circuit with respect to the polarized wave (b) when the distance among the conductor rods is selected less to a degree, and it is equivalent to the absence of the aperture. Thus, the deterioration in the VSWR characteristic of the polarized wave (b) is prevented. On the other hand, since the conductor rods 17a∼17c are made orthogonal with respect to the polarized wave (a), almost no effect is given. Thus, the aperture of the optimum branch part is selected to the polarized wave (a) without deteriorating the VSWR characteristic of the polarized wave (b).