A portable telephone includes a metal substrate, a shield box, a monopole antenna and a feed unit. The surface of the metal substrate includes a conductive metal layer. The shield box covers a radio transmitter-receiver unit provided on the metal substrate to electromagnetically shield the radio transmitter-receiver unit, and has conductivity. The monopole antenna extends in a predetermined direction, and has an electrical length of (.lambda./2).times.N (N is an integer). The feed unit is provided at the metal substrate so as to be apart from the shield box in the extending direction of the monopole antenna. The feed unit includes a matching circuit.