PURPOSE: To ensure an effective debugging with a simple constitution, by setting conditions for each processor to be debugged, detecting the state of a processor coincident with said conditions and supplying the result of the above-mentioned detection to other processors.

CONSTITUTION: Both processors 20 and 30 to be debugged set previously specific addresses respectively. The processor 20 executes a start instruction to the processor 30. As a result, the state of the processor 30 at the starting side is traced when a POST macroinstruction is executed by another processor 30 at a shift register 60-1. While the processing route is traced when the processor 20 gives start at a shift register 60-2. Thus a debugging is possible for both processors 20 and 30.