An artificial magnet conductor includes a dielectric medium, basic cells, each being formed on a side of a front surface of the dielectric medium, and including a conductive patch pattern and a conductive loop pattern formed with a predetermined gap with the conductive patch pattern, a frequency selective surface on which the basic cells are periodically arranged on the front surface of the dielectric medium, and a conductive layer formed on a side of a rear surface of the dielectric medium. A phase change from an incident wave to a reflected wave with respect to the dielectric medium is set as an addition value in which a first phase change in the gap is added to a second phase change between the basic cell of the dielectric medium and the conductive layer. A thickness of the dielectric medium is calculated using the addition value.