1. An emulation method for emulating programs in a system having a target machine and a native machine, and in which data processing is conducted in the target machine with a plurality of programs having a different instruction word set than the native machine, comprising the steps of: a. detecting an interrupt instruction defined in a first program in which an instruction of said target machine is executed; b. determining whether or not said interrupt instruction is an input/output control macro instruction by use of an operand value of said interrupt instruction; and c. if said interrupt instruction is determined to be an instruction associated with an input/output control macro instruction in said step b, bypassing the operation system of said target machine by translating said input/output control macro instruction from said first program into an input/output control macro instruction for a second program, in which an instruction of said native machine is executed, under control of a program for controlling said emulation.