PURPOSE: To prevent stacking of a programmable device, by performing the reset operation or the nonmaskable interrupt operation by a microprocessor when a program runs away.

CONSTITUTION: When the program processing is executed normally, a timer reset pulse 30 is issued from a decoder 3 at intervals of a prescribed time T2 shorter than a prescribed time T1 of a hardware timer 4, and the timer 4 is reset each time, and the output of the timer 4 is not issued. If the program runs away, the timer 4 is overflowed to output the reset operation to an indicating line after the elapse of the time T1 because the timer reset pulse 30 is not issued from the decoder 3. By this output, a microprocessor 2 performs the reset operation. When this operation is impossible, the timer 4 outputs a nonmaskable interrupt signal of the indicating line, and the processor 2 performs the nonmaskable interrupt operation.