We modeled a robot's approaching behavior for giving admonishment. We started by analyzing human behaviors. We conducted a data collection in which a guard approached others in two ways: 1) for admonishment, and 2) for a friendly purpose. We analyzed the difference between the admonishing approach and the friendly approach. The approaching trajectories in the two approaching types are similar; nevertheless, there are two subtle differences. First, the admonishing approach is slightly faster (1.3 m/sec) than the friendly approach (1.1 m/sec). Second, at the end of the approach, there is a `shortcut' in the trajectory. We implemented this model of the admonishing approach into a robot. Finally, we conducted a field experiment to verify the effectiveness of the model. A robot is used to admonish people who were using a smartphone while walking. The result shows that significantly more people yield to admonishment from a robot using the proposed method than from a robot using the friendly approach method.