Disclosed is a projection image generating method for a 3D space. An exemplary embodiment of the present disclosure provides a projection image generating method, including: estimating a plurality of image obtaining poses and a plurality of depth obtaining poses including obtaining positions and obtaining angles of a plurality of obtained images and a plurality of obtained depth values obtained in an actual 3D space, respectively, with respect to a reference coordinate system; obtaining a user pose including a location and an angle of the user in a virtual 3D space corresponding to the actual 3D space with respect to the reference coordinate system; and generating a projection image obtained by projecting the plurality of obtained depth values into at least one of the plurality of obtained images, based on the corresponding image obtaining pose corresponding to the user pose and at least one corresponding depth obtaining pose.