A coordinate input device is associated with a liquid crystal display to detect a touch or contact thereon. A transparent board is arranged on the screen of the display to provide a coordinate input surface having a substantially rectangular shape. At least one vibration detector (e.g., a microphone or piezoelectric element) is attached onto the board to detect vibration or sound that occurs when a position input member is brought into contact with the coordinate input surface at an arbitrary input position. The input position is represented as one-dimensional coordinate based on outputs of two vibration detectors, or it is represented as two-dimensional coordinates based on outputs of three vibration detectors. Thus, the manually designated input position is detected and is electronically displayed on the screen of the display. As the position input member, it is possible to use a pen, a fingernail, etc.