Abstract: The present invention is a sitting device that gives the user an option to sit with one side of his/her lower portion of the body (e.g., buttock, thigh and leg) supported by a half seat, while maintaining a standing posture with the unsupported leg. Since the standing posture naturally keeps the lumbar lordosis, the device eliminates the source of sitting-related back pain. In an embodiment, the sitting device includes two half seats that can be raised or collapsed individually, and a foot stool for the foot to rest in case it is raised. The user can change the positions of the half seats manually by pushing one of the provided buttons. Or it can be automatic if the user uses a controller to program how frequently the half seats alternate, or both of them be in supporting position at the same time to use the device as an ordinary chair.