When you operate buttons on electronic devices, you often hear a feedback sound like a "beep". Recently, a lot of touchscreens are used as user interfaces (UIs) on electrical devices, but a touchscreen doesn't give tactile feedback. In addition, there are two kinds of touchscreens; those which can give visual feedback and those which can't. In this paper, we evaluated the effectiveness of operation feedback sound on touchscreens. We prepared five kinds of software applications, all with

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... t sound timings of feedback sound, including one without sound. Using these applications, we carried out two experiments, one with visual feedback and the other without. As a result, we found the following: (1) operation mistakes can be reduced by a feedback sound, (2) operation time is reduced mainly by visual feedback, however, feedback sound can reduce operation time on the UI without visual feedback, (3) regarding operation feeling, users feel uneasiness or uncertainty without a feedback sound, and (4) the best sound timing is to only have a feedback sound when a button is touched. We are going to make some guidelines for Sound UI design including these results.