PURPOSE: To improve the processing speed of a CPU which can execute instantaneously a bug check by collating point discrimination data generated by the CPU in each point and point discrimination data held in a register means and generating selectively an interrupting signal to the CPU.

CONSTITUTION: Whenever a bug is detected in a use stage, a hook number (hi) of a point of this side of the bug is written successively in hook number registers RG1 - RGn in its detected sequence. In such a state, at the time of executing a ROM program, when it reaches each point, a CPU 18 outputs its hook number (hi) onto a data bus 12, and simultaneously, writes it in a register 20. Its hook number (hi) is given to comparators CP1 - CPn from the register 20, and in each comparator CPj, its hook number (hi) is compared with a hook number (hj) held in a hook number register RGj. In such a way, the time required for a bug check is minimized and a processing speed of the CPU is improved.