PURPOSE: To freely set data length and to perform fast data transfer by setting sent data length in an address counter, and disconnecting the data transfer from a CPU and performing the transfer under control based upon the address control outputted by the address counter.

CONSTITUTION: The data of a 1st storage means 41 are sent out according to the address outputted by a 1st counting means 21. The transmission of the data stops when the output of the 1st counting means 21 reaches the value set by a data length setting means 31. For data reception, a 2nd counting means 22 is actuated with a data transmission signal sent simultaneously with the data. Then a 2nd switching means 52 is switched with its output to switch the control of the 2nd storage means 42 to control from the 2nd counting means 22, and the received data are written in the address of the 2nd storage means 42. Consequently, the data length can freely be set and the communication speed can be made fast.