To maintain low VSWR in a use frequency even with the effects of human body, etc., and variation in a part characteristics, by lowering and heightening the resonance frequencies of an antenna coil and an exciter from the use frequency by a prescribed frequency, respectively.

This device consists of an antenna coil 21 whose element length is λ/2 and an exciter 31 which performs impedance conversion (antenna side, one hundred Ω or more is converted to device side 50 Ω). In such a case, for instance, when a use frequency is 1.9 GHz at fc in the coil 21, element length effective length) is set to λ/2 of a frequency f2 that is shifted to an upper side than the fc by 50 to 100 MHz and it resonates to the frequency f2. On the other hand, in the exciter 31, conductor length (electrical length) is set to λ/4 of a frequency f1 that is shifted to a lower side than the fc by 10 MHz and it resonates to the frequency f1. Then, the VSWR characteristic of the device drops in the range from f1 that is lower, to f2 that is higher than the use frequency fc as the center frequency and a band is expanded.