In this research, we propose a World in Miniature (WIM) -based technique for object placement in MR space. We considered that this would make it possible to freely place objects in 3D space, and to immediately check the position of objects that have been rearranged. In our prototype, we used the mesh of the room provided to represent the occlusion relationship by the MR device to generate a 3D miniature model of the room. We also made it possible to manipulate the virtual objects in the room by manipulating the miniature objects in the miniature model. In order to obtain a guideline for future system design, we conducted an experiment to investigate the characteristics of the manipulation of miniature objects in MR. The results showed that the manipulation of miniature objects in MR is effective in object searching, moving, and reducing physical workload, but that scaling manipulation is difficult. The results also suggest that these effects are affected by the viewing angle and the accuracy of hand tracking of the MR device, and provide guidelines for future system design.