A handwriting input device includes a hollow charger and a handwriting pen. The charger includes a number of first contacts and a connecting unit. The handwriting pen includes a number of second contacts, a communication unit, a light source to emit light, an optical sensor, and a microcontroller. When the charger is connected to an external electronic device through the connecting unit, and the handwriting pen is inserted into the charger to cause each second contact to be contacted with one first contact, the handwriting pen can obtain power from the external electronic device. When the charger is moved, together with the handwriting pen being charged, the optical sensor converts the light reflected from a reflective surface under the charger into the electrical signals. The microcontroller generates and transmits the cursor control signals or the track control signals to the external electronic device.