A touch device is disposed on a substrate having a plurality of gate lines. The touch device comprises a power line, a photo sensor and a readout line. The photo sensor is electrically coupled to the power line and two specific gate lines of the gate lines, and generated a different output signal according to irradiation with a different level. The readout line is electrically coupled to the photo sensor for outputting the output signal. The photo sensor comprises a readout switch and a photosensitive switch. The readout switch is electrically coupled to one of the two specific gate lines. The photosensitive switch is electrically coupled to another of the two specific gate lines and the power line. Signals in another of the two specific gate lines and the power line cooperate to determine whether the photosensitive switch is in an off state.