To attain improvement in operability and to prevent erroneous connection caused by erroneous operation in the case of making a call from a public telephone set to a party using a portable telephone set or the like.

After a portable telephone set 3 is connected to a cable 5 connected to a public telephone set 1, when a user hooks off the public telephone set, inserts a call tariff and operates the number of the party out of a telephone directory in a memory 35 by operating an operating part 34 of the portable telephone set, the portable telephone set transmits this number of the party through a public telephone set interface 32 and a cable to the public telephone set. When the number of the party is received, the public telephone set automatically makes a call through a line interface 12 to that number of the party and calls the party. When the party responds to this call, the user starts talking with the party through the portable telephone set 3.