PURPOSE: To trace a common bus and local buses in respective processor modules by a multiprocessor system which meets requirements of the maximum connection number of common buses by enabling tracing operation and tracing all the common buses.

CONSTITUTION: A trace interface 8 transfers local bus trace data from the respective processor modules 31, 32, and 33 to a trace memory 4. A timer value is set in a trace timer 6 and a trace control part 5 controls the trace timer 6; traces both the data of a common bus 1 and data of a local bus 20 at the same time or traces one optionally selected bus, and stores trace information in a trace memory 4.