PURPOSE: To improve the using efficiency of buffers by using again the buffers so far used at and after the head one in case an error is detected during the input of data.

CONSTITUTION: The head address of a buffer to be used is set to a register/ counter 7 provided in an input data transfer part 5 from an empty buffer pre- reading part 6. Thus the input data are written successively with an address shown by the counter 7 used as the head address. While a controller 13 holds a buffer descriptor identifier of an input start mode at a register 20 when the input of data is started. If an error detector 18 detects an error of the input data during the input of data, the controller 13 controls a switch 19 to produce a buffer descriptor address from the value of the register 20 and defines this address as the head address of the buffer to be used next.