16. A character input apparatus for automatically switching an input mode in a terminal having a touch screen, the character input apparatus comprising: a memory configured to store character groups, each of which includes at least two characters, displayed in at least two key regions acquired by dividing a region of the touch screen based on one-to-one correspondence; a touch screen configured to display the character groups in the key regions based on one-to-one correspondence and generating a press event, a release event, and a drag event according to user input to each of the key regions; and a controller configured to: determine whether the drag event occurs prior to occurrence of the release event if the press event occurs in a first of the key regions of the touch screen; execute one of a separate input mode for inputting one of characters of a corresponding character group and a text input mode for inputting a word including one of the characters of the character group according to whether the drag event occurs; and upon execution of the separate input mode, assign each character of the character group associated with the first key region to a different one of the key regions other than the first key region and display the characters of the character group in the other key regions.
16. A character input apparatus for automatically switching an input mode in a terminal having a touch screen, the character input apparatus comprising: a memory configured to store character groups, each of which includes at least two characters, displayed in at least two key regions acquired by dividing a region of the touch screen based on one-to-one correspondence; a touch screen configured to display the character groups in the key regions based on one-to-one correspondence and generating a press event, a release event, and a drag event according to user input to each of the key regions; and a controller configured to: determine whether the drag event occurs prior to occurrence of the release event if the press event occurs in a first of the key regions of the touch screen; execute one of a separate input mode for inputting one of characters of a corresponding character group and a text input mode for inputting a word including one of the characters of the character group according to whether the drag event occurs; and upon execution of the separate input mode, assign each character of the character group associated with the first key region to a different one of the key regions other than the first key region and display the characters of the character group in the other key regions. 18. The character input apparatus of claim 16 , wherein the controller determines whether a key region indicated according to distance and direction of the drag event is the same as one of the key regions where the characters of the key region where the press event occurs are displayed, highlights the indicated key region if it is determined that the key region is the same as one of the key regions, and outputs a character of the key region where the release event occurs onto a predetermined input editor window of the touch screen if the release event occurs in the highlighted key region.