An antenna coil 10 comprises an air-core coil 12 which is wound helically in a plane and a plate
magnetic core member 13 which is inserted in the air-core coil 12 so as to be approximately parallel with a plane of the air-core coil 12. The
magnetic core member 13 is formed by a soft magnetic
metal, an amorphous or ferrite, or a composite member of a
powder, flake and plastic, or rubber. The
magnetic core member 13 is formed by performing an injection molding operation or a compressing molding operation of the composite member. Alternatively, the magnetic core member 13 is a
magnetic coating which is formed by applying and
drying the composite member. A non-magnetic conductive plate 14 which has a
conductivity is layered on a surface of the air-core coil 12 through which the magnetic core member 13 is inserted. The conductive plate 14 is made of a
copper, a
copper alloy, an aluminum or an aluminum
alloy having 0.01 to 2 mm thickness. By doing this, it is operated by relatively
high frequency while it is rigid relatively.