A digital processor having a key input unit and a key input method are disclosed. The key unit includes: a base that is fixed at the central position of the key unit; a slider that horizontally moves in parallel to the horizontal plane of the base by the user's operation; a frame that supports the slider so as to horizontally move; and a restoration unit that gives a resistive force against the horizontal movement of the slider and restores the horizontally-moved slider to an original position. Accordingly, it is possible to reduce the number of keys by increasing the number of information to be input by the use of a single key.