This invention relates to a single-hand input keyboard for inputting data into various data processing devices, which can be held and operated by a single hand. The keyboard includes a case having an upper case and a lower case, the upper case having an opening at a central portion thereof, a switch unit mounted in the case, the switch unit having a plurality of button switches facing the opening, and a holder formed in a back face of the case. A plurality of the button switches are arranged so as to be pressed by fingers when the single-hand input keyboard is held by a single hand with the thumb and the palm.