Abstract: A handwriting input device includes a shell, a refill, a light emitting unit, a pressure sensing unit, a light sensing unit, a track determining unit, and a transmitting unit. The refill includes a nib and a distal end. The light emitting unit emits light on a writing medium. The light sensing unit captures images on the writing medium and analyzes the images to obtain a track of the nib. The pressure sensing unit senses whether the nib writes on the writing medium. The track determining unit determines a writing track based on the track of the nib and a sensing result of the pressure sensing unit. The transmitting unit transmits the writing track to an electronic device. The writing track is used to determine an input operation of the electronic device.