There is provided a radio apparatus which includes an antenna device and a housing to which the antenna device is attached. The antenna device includes a substrate includes an electrically conductive layer with a slit. The slit is formed at an end of the electrically conductive layer so that the slit includes an opening end. The antenna element is electrically coupled with the electrically conductive layer across the opening end via a matching circuit, and receives an electric power through one end of the antenna element.