Methods of measuring characteristics of an object to be measured, and flat plate-shaped periodic structure

The present invention maintains the object to be measured in a plate shape of a periodic structure (1) is irradiated with electromagnetic waves of linearly polarized light to the periodic structure (1), forward scattering in the periodic structure (1) or a measuring method for measuring a characteristic of the object to be measured based on changes in the backscattered wave, the periodic structure (1), the unit structure of the same shape, in the direction of one reference plane a two-dimensional and periodic structure comprising a plurality of connected, the unit structure has at least one gap portion (11) penetrating in a direction perpendicular to said reference plane, said electromagnetic wave it is irradiated from a direction perpendicular to the reference plane, the shape of the unit structure, a shape that do not mirror symmetrical with respect to a virtual plane orthogonal to the polarization direction of the electromagnetic wave, a measurement method.