PURPOSE: To realize a coexistence of a nesting processing without rewriting other existing machine language instruction train part by providing the first machine language instruction on the tip of a nesting.

CONSTITUTION: Contents (n) of a sleded code train SC shown by contents 4 of a register R are shifted to a program counter PC, and contents of R are added by "1" and updated. As for an indirect jump, a code P is fetched to an instruction register IR in the same way as the case when execution of a machine language instruction train is performed. After the fetch, the contents of PC are added by "1" and become (n)+1. When executing the machine language instruction P, first of all, contents 5 of the register R are pushed into a stack STK. Subsequently, the contents (n)+1 of the counter PC are shifted to the register R, a sleded code (c) indicated by the register R is loaded to the counter PC, and also the contents of the register R are added by "1", and updated so as to indicate the next address. In this way, a nesting is transferred to a sleded code train SC-1.