An array substrate according to the invention includes an external terminal formed in the vicinity of an end portion of an insulating substrate so as to supply electric potential from the exterior to a driving circuit, a signal line monitoring terminal formed in parallel with the external terminal, a signal line branch terminal formed in such a way as to be connected to a signal line or to a signal line terminal, and an internal terminal associated with the signal line monitoring terminal, which is connected to the signal line monitoring terminal and connectable to a signal line branch terminal by an electrically conductive material and a bump of the driving circuit.