1. A method of generating an environment map for generating an environment map concerning an environment in which a mobile robot moves, the environment map specifying an obstacle area in which an obstacle exists and a movable area in which it is estimated that the mobile robot is movable, the method comprising: generating a three-dimensional position data set indicating a position of a measurement object existing in the environment, by using measurement information obtained from a vision sensor; selecting, based on an old environment map which is the environment map generated in the past and an amount of movement of the mobile robot, at least three-dimensional position data belonging to an area determined as the obstacle area in the old environment map, and three-dimensional position data belonging to an unobserved area which is not included in the old environment map, from among three-dimensional position data included in the three-dimensional position data set, as plane-detection target data; performing plane detection using the plane-detection target data; recognizing the movable area and the obstacle area which are included in the plane-detection target data, by using results of the plane detection; and generating a new environment map which is an environment map newly generated by integrating the movable area and the obstacle area, which are recognized using the results of the plane detection, with an area determined as the movable area in the old environment map, wherein the plane-detection target data does not include entire three-dimensional position data belonging to an area determined as the movable area in the old environment map.