A new designing approach based on object-oriented method is proposed to design a unique but rather complicated virtual environments the salient feature of which is that a human-shaped virtual instructor can behave like a real instructor to educate a trainee about the complicated tasks such as machine maintenance work and plant operation. The advantage of the proposed approach is that it allows the developer to construct various virtual objects for the targeted virtual environment flexibly by combining the components which are independently constructed in advance. In this paper, the elemental technologies used for the object-oriented approach are described such as to realize a virtual instructor, how to design the virtual environments with the object-oriented method and how to configure the system of executing the simulation of the virtual environment.