1. A key device of an electronic device, the key device comprising:a housing in which a key hole is formed;
a side key unit assembled at the key hole of the housing; and
a gap of a predetermined thickness formed between a portion of the assembled side key unit located within the key hole and the key hole,
wherein the gap is secured by processing either or both of the side key unit and the key hole, and
wherein the gap comprises a coating in order to reduce a surface tension of the gap.