The present invention provides a measuring method comprising the steps of holding a specimen on a flat-plate periodic structure, applying a linearly-polarized electromagnetic wave to the periodic structure, and measuring characteristics of the specimen based on change of the electromagnetic wave scattered forward or backward by the periodic structure, wherein the periodic structure is structured such that plural unit structures having the same shape are two-dimensionally and periodically interconnected in a direction of one reference plane, the unit structure has at least one aperture penetrating therethrough in a direction perpendicular to the reference plane, the electromagnetic wave is applied from a direction perpendicular to the reference plane, and the unit structure has a shape that is not mirror-symmetric with respect to an imaginary plane orthogonal to a polarizing direction of the electromagnetic wave.