We define "BITAIKA" as a self-posture adjustment system while sitting in order to correct a posture. We developed BITAIKA with visual feedback as a first step and found out it may be effective to correct a user's posture with visual assistance [Ishimatsu and Ueoka 2014]. However in order to correct its posture by refining its muscle structure, it is necessary to use it for long term. In that sense, it is not sure if visual feedback is adequate because we usually do computer or paper work while sitting and as we concentrate on the work we easily ignore the notification action from the system. So in order to find the right feedback for BITAIKA, we implemented a system to give stimuli to a user's back to notify the timing to correct its posture. We conducted the experiment to compare the effectiveness between visual and backstimuli feedback.