To provide the track ball device of a note-sized computer for mounting a track ball device in a size available even to a thin note-sized computer by separating a ball from the track ball device main body, and for fetching a password or an ID or a function such as a power supply switch.

In the ball separation type track ball device of a note-sized computer, a ball is separated from a track ball device, and a ball separation type track ball device 2 without any ball is mounted on a note-sized computer 1, and at the time of using the note-sized computer 1, a ball unit 3 is mounted on the ball separation type track ball device 2 afterwards.