We have developed an automatic code generator which generates C language code from object-oriented specification diagrams. It reduces the target program size 35% smaller than the size of the program which was simply translated into C++ code. We accomplished this effective optimization by removing some mechanisms of object-oriented programming languages which are unused for our target application, embedded real-time software. Object-oriented programming languages provide many useful features such as inheritances, constructors, destructors, virtual tables and instances. But software of small embedded real-time control systems does not need all of these features, because the end products must be on ROM of one-chip controllers and the runtime behavior of the software is fixed. We remove the unused mechanisms of object-orientation by considering the feature of the target application to reduce the size of the programs.