To provide an antenna that converges for receiving an electromagnetic signal at a microwave and millimeter wave band.

A visually transparent diffraction structure 3 which acts as a Fresnel lens is fitted to a window 2 for receiving and converging a television signal 5 from a satellite 4, and the converged signal is delivered in the inside of a building 1. The distribution of energy density of electromagnetic waves in a spatial region specified by the structure is concentrated in the inside of the building 1 or an internal space after the diffraction structure 3. The diffraction structure 3 is designed to be unchanged with respect to time to be in matching with reception of a prescribed signal only. In addition, the structure is changed so as to be adaptive in various reception states such as revision of a reception frequency and of a reception frequency by controlling a dielectric characteristic of its local element. Thus, in this way, an adaptive interface is formed between an external space and the inside for the signal reception.