PURPOSE: To prevent a failure of a frame transmission, and to improve the transmission efficiency by interrupting to send out data in an event generation period and sending out an interrupting signal which has been defined by a prescribed control code, in case when an event which necessiates a frame transmission stoppage has been generated.

CONSTITUTION: A transmission control part 14 in a communication controller 12 reads out transmission data from a buffer memory 11, constitutes a frame and sending it out to a transmission line 20. In the course of such a frame transmission, if such an event as the frame transmission must be stopped is generated in the inside or the outside of a communication controller 12, the transmission control part 14 receives a frame interrupting command from a frame interruption detecting part 13, interrupts to send out the data to the transmission line 20, and sends out an interrupting signal instead of sending out the data. When the event which necessitates a frame transmission stoppage annihilates, the transmission control part 14 receives a frame restart command from the frame interruption detection part 13, stops sending out the interrupting signal to the transmission line 20, and restarts to send out the data from the succeeding data.