PURPOSE: To perform debugging on a multi-CPU type device efficiently through one console by supplying an enable signal from a selector and operating only a specific serial-parallel converting circuit.

CONSTITUTION: Only one console 21 is used for debugging operation and its connector 22 is connected to the connector 23 of the multi-CPU type device 10. The enable signal is supplied from the selector 30 to operate only the specific serial-parallel converting circuit 11, which converts serial data from the console 21 into parallel data. Thus, a debugging signal from the console 21 is supplied to only the CPUs 12 of specific function units 1 - 3. Consequently, only one console 21 is provided to supply the debugging signal from the console 21 to the function units 1 - 3 independently in order without any mechanical switching.