PURPOSE: To suppress the increment of execution time for data transfer by separating a control board detected at its abnormality from other control boards on the receiving side at the time of its detection and switching current data transfer to 1 to 1 type data transfer to continue the data transfer.

CONSTITUTION: If a control board 1 receives an error signal from a control board 2 when the board 1 executes 1 to 2 type data transfer through a common bus 15, a control information changing means 10 is actuated and an address of the control board 2 transmitting the error signal out of addresses specified by the control information is erased. Afterthere, the control board 1 executes 1 to 1 type data transfer to a control board 3. After the end of the data transfer, data transfer from the control board 3 side to the control board 2 side is executed, so that the operating time of the control board 1 having a channel interface function can be reduced.