The present disclosure relates to a metasurface structural body or the like having a structure for achieving desired optical characteristics. The metasurface structural body includes a base member having a first surface and a second surface opposing each other, and a plurality of antennas as a plurality of fine structures arranged along the first surface. The base member has a base portion and an adjacent portion. The antennas each has a first refractive index and an antenna end surface constituting a part of the first surface. The adjacent portion is provided such that a part thereof is positioned between the antennas, the adjacent portion having a second refractive index different from the first refractive index and an adjacent-portion end surface constituting a remaining part of the first surface. The antenna end surfaces and the adjacent-portion end surface form a flat surface as the first surface.