PURPOSE: To stop the execution at the optional position of a program, and to improve the efficiency of debugging of the program by comparing the contents of a data comparing register and the value set to a program counter, with a reference value from the outside.

CONSTITUTION: The value set to a program counter 8 is transferred to an address register 1 through a data bus 101, and an instruction is read out of a program memory 2, and set to an instruction register 3. When it is an operating instruction, an operating data is read out by designating the first and the second data registers 5, 6, operated by an operator 7, and its result is sent to a register corresponding to the instruction through the bus 101. In this case, the output of the first comparator 9 and the output of the third comparator 12 are sent out to a clock controlling circuit 13, and in case both coinciding circuits detect coincidence, an FF in the controlling circuit 13 is set, an inversion output is reduced to "0", a clock from the controlling circuit 13 is not sent out, and the execution of instruction stops.