PURPOSE: To enable judgement when charging during the non-communication period exceeds the constant amount of money without a user setting the unit charging time and the monitoring time in advance and to automatically disconnect the line by learning the unit charging time by using the information accepted from the communication destination and the network.

CONSTITUTION: A call control means 330 starts monitoring by a radio communication means 332 when the logical channel is set. How many charging in the communication unit is performed from the line connection to the disconnection is performed. Then, whether or not further communication can be performed in the present charging number while waiting for the constant time is judged. When the line connection time is short, the communication is continued. When it is long enough, the disconnection of the logical channel is reported from the means 33 to the means 330. Thus, the ISDN line is opened according to the protocol decided by the means 330 to estimate the rise of the communication charge and the line is disconnected just before it.