PURPOSE: To extend the time of instruction tracing, by comparing input data with data stored in a collation memory, and not writing input data in a memory for tracing if the data is stored in the collation memory.

CONSTITUTION: Pairs of a specific number of branch instruction addresses, which are inputted latest, and branch destination addresses for them are stored in a separate high-speed access memory 4; and if a pair of a branch instruction address and a branch destination address which should be stored newly is stored already in the memory 4, the pair is prevented from storing in a memory 6 for tracing.