PURPOSE: To minimize the system down state at the time of the occurrence of a prescribed fault in the middle of data communication.

CONSTITUTION: A line releasing means 16a which releases a line at the time of receiving a message for call disconnection from the network side in the middle of data communication, a disconnection reason discriminating means 16b which discriminates whether the disconnection reason of the message for call disconnection is prescribed one, and an automatic call originating means 16c which automatically conducts the call originating operation after a prescribed time are provided. When the call is disconnected because of the occurrence of a fault on the network side in the middle of data communication, the call originating operation is automatically conducted the prescribed time after the disconnection if this disconnection is caused by the prescribed reason, that is, if it can be recovered in a short time, thereby restoring the data communication state as soon as possible.