There is known a technique of adding a corresponding image to the real space, which is called augmented reality (AR). For example, Patent Document 1 describes a virtual image stereoscopic synthesis device capable of displaying three-dimensional shape information of an arbitrary object in a real space to which an observer belongs. Further, Patent Document 2 describes a head-mounted display capable of displaying an object relating to a target present in an external world viewed by a user.
Patent Document 1: Japanese Patent Application Laid-open No. 2000-184398
Patent Document 2: Japanese Patent Application Laid-open No. 2012-053643