This study addresses encounter interactions in public environments where people and robots walk around. In daily life, security guards, police officers, and sales clerks roam around environments and nonverbally present friendly behavior so that people feel comfortable talking to them. We modeled the behavior of human experts during friendly patrolling, which we defined as a roaming behavior that nonverbally presents a friendly attitude, to encourage people to talk to such professionals. The model was implemented in a humanoid robot, Robovie, and tested in a shopping mall. The experimental results with 39 participants demonstrated that the model worked as intended.