To provide a radio card reader/writer that is configured at a low cost by using a specific frequency regulated by the law of electric communication services and satisfying the law of electric through the matching between a design value and an actually measured value of a loop antenna and integrating the loop antenna in a metal-made case.

The radio card reader/writer that transmits power and transmits and receives data to/from a radio card through radio transmission/reception with the radio card of no battery type, uses a loop antenna where a ground pattern 82 is placed along a loop antenna main body 81 while keeping insulation with the loop antenna main body 81 (with a printed circuit board 83 inbetween) on one face of the loop antenna main body 81 with a prescribed aperture area and the ground pattern 82 connects with a ground terminal 81a of the loop antenna main body 81.