The main purpose of this paper is to develop an easy-to-use smartphone case with “fall prevention function”. It shows as a remarkable point that our developed technique of determining the grip form reflecting the traditional craftsmanship verifies for the made-to-order wooden products. It also provides the experimental result of wooden smartphone case using electromyography (EMG). The experiment consists of two cases, with using a smart phone case and not it. Then, it compared with these two cases, the result of measuring the amplitude of gripping forces. The experiment suggests that using the smartphone case relatively clearly that applies significantly less gripping force, so that prevents dropping a smartphone. The experiment suggests that using the smartphone case it applies significantly less gripping force. It will provide a new guideline of the universal design as a case study of Kansei/affective engineering regarding human grip.