A data communication apparatus 1 has a processing section (CPU) 10 that executes at least a part of communication processing of a communication controller 2 and that executes processing other than the communication processing, whereinThe data communication apparatus 1 has an interrupt request blocking section 20 that blocks, during execution of a processing relevant to information exchange concerning a communication condition for the communication controller 2 to carry out a communication processing, an interrupt request to the processing section 10 with priority over the processing relevant to information exchange. With this arrangement, even when additional operation is carried out to execute an interrupt processing during execution of a processing concerning a communication condition such as a modulation system of a modem and a communication speed, the processing can be executed securely and a stable connection of a communication line can be maintained.