In this study, we focused on the changes in balance perception accompanying balancing tasks. The study goals were to propose an experimental method in which subjects experience perceptual changes in balance from a seated posture and present evidence that such changes occur. As balance perception, we considered a psychologically upright posture, a posture at which the upper body feels slanted to neither the left nor right. For the experiment, we newly constructed a special stool. Dynamic environment on this stool with 2 DoFs, the lateral translation and the roll rotation, could change this psychologically upright posture after motor learning in a balancing task.