A cell phone including a built-in antenna, the cell phone having a reduced physical size of an antenna element, a decreased weight and satisfying an impact resistance, and suppressing a variation in a dimension caused by mass production and considering an actual use state in which a hand or the like approaches. A dielectric between an antenna element and a ground is a support member of a cyclo-olefin polymer in a plating grade having an impact resistance which is obtained by blending styrene type rubber, polyolefin type rubber (elastomer) or both of them, and the antenna element is constituted by a plating formed on a main surface of the dielectric.