PURPOSE: To provide the line controller with high reliability especially in the case of high speed transmission by implementing smoothly hand-shake between the line controller and a processor.

CONSTITUTION: The line controller provided with a read/write means storing communication data sent/received synchronously with a transfer speed of the communication data sent through a communication line tentatively in a buffer 3 and implementing read/write of the data stored in the buffer 3 and with a counter 2 counting data quantity stored in the buffer 3 is featured to be devised in such a way that a count of the counter 2 is stored to any of plural registers 15 storing the count of the counter 2 upon the receipt of frame end data included in the communication data and the count stored in the register 15 is sent when a read signal sent from the read/write means is applied to the line controller.