PURPOSE: To attain the control of a break point at a time point when a microcode is read out and the value of a break point control field is equal to '1', by providing this control field to the microcode.

CONSTITUTION: The value '1' is previously set to the control field 40 of a microcode to which the break point control is desired among those microprograms stored in a file memory. Then a start address is set to an address register 6 and the RUN state of a processor is set to a control register 1. Thus the microcodes are successively set to a pipeline register 5 from a storage 4 and then executed. When the microcode having the field 40 set at '1' is latched by the register 5, a clock stop signal is sent to a clock control part 2.