We present a system to allow blind people to stand in line in public spaces by using an off-the-shelf smartphone only. The technologies to navigate blind pedestrians in public spaces are rapidly improving, but tasks which require to understand surrounding people's behavior are still difficult to assist. Standing in line at shops, stations, and other crowded places is one of such tasks. Therefore, we developed a system to detect and notify the distance to a person in front continuously by using a smartphone with a RGB camera and an infrared depth sensor. The system alerts three levels of distance via vibration patterns to allow users to start/stop moving forward to the right position at the right timing. To evaluate the effectiveness of the system, we performed a study with six blind people. We observed that the system enables blind participants to stand in line successfully, while also gaining more confidence.