PURPOSE: To change a built-in predicate without recompiling an existing program again by realizing a machine language instruction realizing the built-in predicate both by a microprogram and a machine program.

CONSTITUTION: When a processing unit 140 fetches the machine language instruction built-in, it sets the execution information of an operand field 220 to a register 170 in a processing unit 140. Then, by using the offset of an operand field 210, the entry of a memory 120 is read. When an identification flag 130 is '1', the value of a program counter 160 is saved in a register 180, thereafter, branches to the machine language program indicated by the entry. When a microinstruction is executed, a processing for the built-in predicate is carried out, thereafter, the next instruction to the machine language predicate built-in is executed.