PURPOSE: To improve the maintenance management efficiency of a data processing unit by providing an adapter having a data buffer line connection control function onto the data processor.

CONSTITUTION: In the case of using a console equipment 9, a data input output section 12 commands a telephone number of a line 8 to which a console connection adapter 2 is connected to call the adapter 2. When a telephone set 7 is not hooked off even with a prescribed number of times of ringing or over, a line connection control section 6 connects the line 8 to a data transmission control section 5 to complete the connection between the equipment 9 and the adapter 2. In this case, the information inputted from the input output section 12 is sent as it is to a data processor 1. Moreover, the information outputted from the processor 1 is outputted as it is to the input output section 12, the input output section 12 acts like a console of the processing unit 1.