A handwriting input apparatus used with an electromagnetic pen is disclosed. The handwriting input apparatus comprises a controller, an electromagnetic antenna board, a signal processing circuit and a charging circuit. The signal processing circuit processes the electromagnetic signals received by the electromagnetic antenna board. The charging circuit used to charge the electromagnetic pen includes a first device which is used to output a first voltage to charge the electromagnetic pen after a voltage of the handwriting input apparatus being inputted. The charging circuit further includes a programmable voltage device connecting to the first device. The programmable voltage device is controlled by the controller to change the first voltage according to the detection of the first voltage by the controller.