PURPOSE: To obtain a portable telephone set connectable to plural switching networks.

CONSTITUTION: A radio base station is selected and the switching network to be connected is set by switching the control channel of the portable telephone set in a switching network system equipped with the radio base stations 16, 17, and 18 with different control channels, the switching networks 13, 14, and 15 connected to those radio base stations, and the portable telephone set 19 connected to the radio base stations by radio. Thereby, the portable telephone set 19 is connected to, for example, the switching network 14 via the radio base station 17, which makes possible speech with an opposite telephone set connected to the switching network 14 to be performed.