We propose a system to construct Mixed Reality (MR) environments based on actual environments. Our goal is to develop MR content in which users and characters can coexist in an actual room and experience a story. This study represents a preliminary step in the development of such an MR experience. We proposed a method to construct an MR environment that uses three-dimensional information acquired from the actual environment based on rules. We extract valid plane information from three-dimensional information and use it. Virtual objects used for MR content can be placed in real space automatically. Rules are created by specifying the area and height of the plane of the real space. In this study, we placed seven types of objects in two types of rooms and confirmed that it is possible to construct an environment using a transmission-type head mount-ed display. However, under the current system, users cannot experience a story.