To provide a circular dual reflector antenna suppressed with sidelobe level due to spillover attributable to diffraction from an end part of the circle of a sub-reflecting mirror.

In the dual reflector antenna, electromagnetic waves are emitted from a primary reflector 4 projecting from the center of the concave surface of a circular concave main reflecting mirror 5 toward the sub-reflecting mirror 2 which is held in front of the primary reflector 4 in such a manner that the circular convex reflection surface may face the main reflecting mirror 5 and then are reflected by the sub-reflecting mirror 2 toward the main reflecting mirror 5 and finally are rereflected by the main reflecting mirror 5 to be emitted into the air. At the back of the circumference of the reflection surface of the sub-reflecting mirror 2, a circular regulator plate 1 is disposed along the circumference which forms a choke having the total length of the round-trip length of the depth and the width of the bottom face combined equal to 1/3 or 2/3 of the use wavelength. To gain more effectiveness, a concentric circular concave portion is formed in the surface of the circular regulator plate 1 facing the main beam.