An environment map building method and an environment map building apparatus can express the surrounding embodiment with a high resolution in the height direction in a manner robust relative to observation noises. The present invention provides an environment map building apparatus for building a three-dimensional environment map to be used for three-dimensionally determining a region allowing a moving body to move therein according to external environment conditions, which comprises an external environment conditions detecting section that detects external environment conditions, a three-dimensional map building section that builds a three-dimensional map showing the state of occupancy of a three-dimensional grid on the basis of the external environment conditions detected by the external environment conditions detecting section, a relative-to-base-plane height map building section that builds a relative-to-base-plane height map showing heights from a two-dimensional base plane on the basis of the external environment conditions detected by the external environment conditions detecting section, and a height map information modifying section that modifies the information of the relative-to-base-plane height map on the basis of the information on the three-dimensional map.