To ensure a high gain and a wide band.

An inverted L-shaped antenna 10 is a feeder device having its one end electrically connected via a feeder point to one plate surface of a circuit board 12. The circuit board 12 is a board for a circuit of a portable radio, to which circuit parts including the inverted L-shaped antenna 10 are connected. A plate-shaped antenna 14 is provided in opposition to a back side plate surface between the plate surfaces of the circuit board 12, to which the inverted L-shaped antenna 10 is connected. The plate-shaped antenna 14 is a non-fed component where longitudinal electric length is about 1/2 of the wavelength of an electric wave with which the portable radio communicates. Sizes and spaces of the inverted L-shaped antenna 10, a circuit board 12, and a plate shaped antenna 14 are adjusted to predetermined values. Further, a self-impedance of the inverted L-shaped antenna 10, a self-impedance of the plate-shaped antenna 14, and mutual impedance between the inverted L-shaped antenna 10 and the plate shaped antenna 14 are changed.