PURPOSE: To realize a high-speed process, by reading the microinstruction with the address produced by the conditions already set up and executing the microinstruction in case a process request is given and at the time point when the rest conditions are set up.

CONSTITUTION: When the signals A, B and C within the circuit control region are on each, the table region of the ROM5 is indexed based on the address produced by the address producing circuit 3. The read-out contents is sent to the circuit 3. The circuit 3 produces the address of the microinstruction region of the ROM5 based on the contents of the circuit control region as well as the contents of the table, and the indexing is carried out based on the address. Then the read-out microinstruction is set to the register 6. On the other hand, the contents of the BSV signal is set to the flip-flop 7 to be held in the form of the FBSV signal. After this, the microinstruction already read out is executed when both the FBSV and M are on.