To provide a flat panel to which a power supply pin is inserted easily and surely in a through-hole and can be joined to, and from which a predetermined antenna impedance is stably obtained.

The flat antenna is the flat panel containing a substrate with a through-hole which consists of a dielectric or a magnetic substance and is penetrated at a rear face from a front surface, a first electrode formed in the front surface, a 2nd electrode formed in the rear face, and the power supply pin inserted in the through-hole. Either cross section profile of the power supply pin and a cross section profile of the through-hole is circular, and a cross section profile of another side is polygon. The power supply pin is inserted in the through-hole so that an inner wall of the through-hole may be touched in a plurality of a periphery.