PURPOSE: To obtain fault information without interrupting the data transfer of other channel parts, by connecting an I/O interface to a service processor in a data processing device provided with an I/O processor and the service processor.

CONSTITUTION: When detecting a fault in individual channel parts, an I/O processor 1 reads out the time from a service processor 3. A pair of the number of the channel, where the fault occurs, and fault information is stored temporarily in a control storage. Fault information in the control storage is transferred to a data buffer of an I/O processor interface part 4 of the service processor 3 in the idle time of the control of other operating channels. The service processor 3 transfers information in the data buffer to a fault information file. Thus, fault information is obtained without interrupting the data transfer of other channel parts.