The purpose of the present invention is to appropriately prevent a decrease in display quality or the like due to breakdown of diode elements of an ESD protection circuit provided in an active matrixsubstrate and a shift in characteristics. Provided is an active matrix substrate that includes a thin film transistor that has a first semiconductor layer and an ESD protection circuit electrically connected with two wires. The ESD protection circuit includes a diode element. The diode element has a first electrode in a gate metal layer, a second semiconductor layer that overlaps the first electrode formed on the same layer of a first semiconductor layer across an insulating layer, and a second electrode and a third electrode electrically connected to a second semiconductor layer in a source metal layer. First and second electrodes of the diode element are electrically connected. The ESD protection circuit further includes a secondary diode structure. The secondary diode structure includesa fourth electrode in the gate metal layer and is in an electrically floating state, and a third semiconductor layer that is formed in the same layer as the first and second semiconductor layers andoverlaps the fourth electrode with an insulation layer in between.