Required time refers to the duration of time that is essential for operators to perform a task, while time available is the time period within which the operators should perform a task. The estimation of operator’s required time is necessary in several human factors-related activities for nuclear power plants (NPPs). Operator’s required time has often been estimated by experiments or structured interviews with instructors, operators, and other knowledgeable experts [3], while the time available is usually estimated by specific approaches, e.g., thermo-hydraulic analysis. Digital main control rooms (MCRs) have distinguished design features from conventional, analog control rooms, including advanced alarm systems, graphic information display systems, computerized procedure systems, and soft control. This change may influence operator’s required time. However, the estimation of required time for the digital MCR has not been studied sufficiently in spite of its necessity. In this study, an approach to estimating operator’s required time for the emergency operation at the digital MCR was suggested by using experiments and Monte Carlo simulation. This study defines the task unit, and develops an ARENA simulation model to describe steam generator tube rupture (SGTR) for Monte Carlo simulation. In this study, required time of isolating a damaged steam generator (SG) was estimated as a result of the simulation.