Java native method is proposed for the efficient execution of time-critical code, running of platform dependent job, and reuse of established libraries. If the writing of the Java native method is the speedup of execution time, you must use a compiled language not java language to write native method. Also, you must know the usage of the Java native interface to use native method. To reduce these difficulties, we proposed java native method generator that changes java method into native method automatically. Also, NMG helps programmer to write C implementation for the native method because there Is no need for the concept of JNI.