``Virtual Collaborator¡Ç¡Ç is an intelligent interface agent to help machine operation controlling a large scale plant system such as power plant. A prototype system of the virtual collaborator has been developed, and the major functions of the present virtual collaborator are that when an anomaly occurs in a plant, the virtual collaborator can autonomously detect it, diagnose the root cause, and operate the control panel in accordance to the operation procedure. The designed function of the virtual collaborator is validated by demonstrative simulation on a distributed computer network. The implication of this virtual collaborator experiment is discussed with respect to the human-centered automation.