Conventional automatic doors cannot distinguish between people wishing to pass through the door and people passing by the door, so they often open unnecessarily. This paper describes an intelligent door system that observes people near a door so that the door opens at the proper time and only for people who have the intention of passing through it. To achieve this, we developed a novel laser range scanner that scans the surrounding environment three dimensionally, and formulated lightweight algorithms for the sensor. The experimental results show that the sensor can control a door according to the speed of people within the required specifications and that it correctly identifies people passing by the door.