A VR (Virtual Reality)-based cooperative training system is proposed for machine maintenance in the nuclear power plant. The NETCOM (NEtworked-vr based Training system for CoOperative machine Maintenance) system has been developed on basic software called LASNET (Large Scale Networked virtual EnvironmenT), which can offer flexible CSCW environment for networked virtual environment with multimedia communication between participants. The interface for cooperative training has been constructed based on ¡ÇHuman-centered Design for VR system¡Ç, and it was verified by an experiment that the NETCOM system would give a sensation of presence in the course of participated training among the users.