This article discusses observation planning for identifying each person in indoor living environment such as office space using a mobile camera mounted on a drone. Since many people in the environment often keep their positions and postures during their work, it is difficult to observe the face of all the people by a fixed camera installed in the environment to identify each of them, when some of them keep orienting their faces toward the directions opposite to the camera. In this article, it is proposed to observe each person’s face with a mobile camera mounted on a small drone, which flies around the ceiling in the environment. Assuming that the position and orientation of each person has already been obtained by the fixed camera, the proposed method observes each person’s face from the front with an appropriate distance in turn while minimizing the total cost for changing the position and the orientation of the drone before completing the observation for all the people.