To reduce loss of a Rotman lens.

The Rotman lens includes a ground plate 80 composed of a conductive member, a dielectric substrate 70 placed on the ground plate 80, and a plurality of input ports 11-15 and a plurality of output ports 41-47 arranged at positions facing the ground plate 80 while holding the dielectric substrate 70. Waveguides 51-56 for leading a signal input to one input port, to a plurality of output ports along the line segments, connecting both ends of the plurality of output ports 41-47 and one input port, are disposed in the dielectric substrate 70 so as not to interfere mutually.