A key input method for diversifying key functions in a mobile telecommunication terminal. The method according to the present invention includes the steps of detecting whether or not a user has inputted a key, detecting whether or not the user has consecutively inputted the same key before elapse of a predetermined time, and if so, performing a function newly set according to the consecutive input of the same key. The method further includes the steps of detecting whether or not the user has inputted a key set for a scroll function, and if so, detecting whether or not the key input state of the corresponding key is maintained for a predetermined period of time, and controlling a cursor positioned at a particular item of a menu screen displayed according to a maintenance of the key input state for the predetermined period of time to be positioned at a next menu item in an opposite direction.