A potable terminal device comprises an upper housing including a display unit on the surface thereof and a lower housing including a hard key on the surface thereof and relatively slidably coupled to the upper housing. Bothe of the housings are movable between a closed position in which all hard keys of the lower housing is covered with the upper housing, at least one intermediate position in which part of the hard keys are uncovered with the upper housing, and a full open position in which all of the hard keys are uncovered with the upper housing. In the intermediate position, in response to pressing any of part of the hard keys which are uncovered, a soft key for complementing part of the hard keys which are uncovered is displayed in a position starting from the edge of the display unit adjacent to the hard keys.