The apparatus has a transformable substrate having a flat state, a deformed state, a partially deformed state, and the like, and thus provides a function and a user interface that change according to the deformed state when a user wears the apparatus on his or her wrist and the flat extended state when the user detaches the apparatus from his or her wrist. When the method suggested in the present invention is used, the user can conveniently carry the apparatus on his or her wrist and use the apparatus on or off the wrist as necessary, thereby resolving inconveniences of carrying and using an existing mobile apparatus.