PURPOSE: To facilitate an analysis of fault and a program test by storing an address where a branch instruction exists to a branching origin storing memory set immediately before an instruction serving as the branching destination an unconditional or conditional branch instruction within a program storing memory area.

CONSTITUTION: When a program of a program storing memory 3 and a branch instruction 4 are executed, the branching origin address is stored in a branching storing origin memory 5 of the memory 3. If a problem such as a program fault, etc. occurs after execution of the program, the memory is traced reversely. Thus it is immediately understood which part the program is executing to reach the relevant faulty area.