A controller of an in-cell type liquid crystal display device is provided. The controller controls first and second electrodes that intersect each other, supplies a pixel driving voltage to the first electrodes during a pixel driving period, and detects a stylus position using the first and second electrodes during a stylus detection period different from the pixel driving period. The controller transmits, using the second electrodes, a command requesting a transmission of a downlink signal to the stylus. The controller detects, using the first and second electrodes, the downlink signal transmitted from the stylus in response to the command, and detects the stylus position based on the detected downlink signal.