To make the dimension of an electrostatic protection circuit small with the same maintained high in sensitivity. The electrostatic protection circuit is of the configuration that a first diode and a second diode are connected in series, wherein a semiconductor layer owned by each diode is configured to be sandwiched between a gate electrode and a conductive light shielding film. The light shielding film is formed to overlap with the semiconductor layer and has a wider area than the semiconductor layer. This results in having a gate covering the semiconductor layer from an upper side and a back gate covering the semiconductor layer from a lower side, so that the sensitivity can be maintained high irrespective of decreasing the electrostatic protection circuit in dimension.