A measuring method that includes holding a specimen to be measured on a flat-plate periodic structure, applying a linearly-polarized electromagnetic wave to the flat-plate periodic structure, detecting the electromagnetic wave scattered forward or backward by the flat-plate periodic structure, and measuring characteristics of the specimen on the basis of a phenomenon that a dip waveform appearing in a frequency characteristic of the forward-scattered electromagnetic wave or a peak waveform appearing in a frequency characteristic of the backward-scattered electromagnetic wave is changed with the presence of the specimen. The flat-plate periodic structure is a flat-plate structure in which at least two voids penetrating through the structure in a direction perpendicular to a principal surface thereof are periodically arrayed in at least one direction on the principal surface, and the electromagnetic wave is applied to the principal surface of the flat-plate periodic structure from the direction perpendicular to the principal surface.