Patent US 5,113,501

An apparatus capable of checking the validity of a microprogram, includes an initializing unit for initializing data representing the validity of each microinstruction of a microprogram to be tested (the validity indicating that each microinstruction is executed), an updating unit for updating the validity data associated with a microinstruction executed when the to-be-tested microprogram is executed, and a reading unit for reading out the validity data when execution of the to-be-tested microprogram is completed.