AbstractEfficiency and reliability are essential to microprograms, and it is important to perform debugging and evaluation through interaction with the simulator. The simulator is also indispensable in the development of the microprogram in parallel to the hardware. However, if a dedicated simulator is to be developed for each target computer, constraints are imposed on time and cost, making it difficult to realize a high‐level interactive interface. On the other hand, if a general‐purpose simulator is to be employed, it is difficult to provide an interface suited to the target computer, such as visual simulation. This paper proposes an object‐oriented system aiming at the realization of both the detailed function of the dedicated simulator and the versatility of the software. Although the object‐oriented language has a high modularity, adequate modeling must be provided for the whole system including the interfaces, to ensure the machine‐independence of the microprogram simulator, where the object of the description itself depends on the target computer. In this paper, an interactive interface is proposed, which is suited to the debugging of the microprogram. Then a realization by the object‐oriented scheme is described which has a high flexibility against the modification of hardware specification and permits an easy reuse of the software for other computers. As a practical example, the development of μP simulator by the authors is outlined, together with the description of the us