In a portable radio apparatus, the antenna performance is improved while fitting conductor elements into an inside of a case without an increase in size of the case when two cases are closed. A monopole antenna arranged in an inside of a first case of a portable radio apparatus includes an element 11 on the power feed side, an element 12 on the open end side, and a resonance circuit 13. A width of the element 12 on the open end side, which comes close to an electronic parts 10 arranged in an inside of a second case and containing a metal in a folded mode, is set smaller than a width of the element 11 on the power feed side, which does not come close to the electronic parts 10.