PURPOSE: To make a time constant till the confirmation of transmittal is attained when a data is sent through the use of any communication line and to decentralize a load with respect to a communication line by calculating the ground of communication line selection based on a reply time of an actual communication line.

CONSTITUTION: A communication line dependent transmission reception management selection means 12 being a selection means selecting one of communication line dependent transmission reception management sections receiving a data to be sent from the communication line dependent transmission reception management sections 3, 4 selects the communication line dependent transmission reception management section having a reply time calculation means calculating a minimum value of expected values in reply time calculation means 36, 46. Thus, the selection of the communication line is realized by taking the difference from the reliability of the communication lines and from the processing capability of an opposite communication equipment into account and the time till the transmittal is confirmed is constant even when a data is sent through the use of any communication line and the load of the communication line is decentralized.