An active matrix substrate capable of suppressing a change in an off characteristic of the TFT even when current passage time becomes longer is provided. A diode is connected between a video signal line and a conductive plate formed so as to cover a TFT of a pixel formation portion. Current is passed to the diode when a potential of a video signal applied to the video signal line is lower than that of the conductive plate, and the potential of the conductive plate becomes equal to that of the video signal line. No current flows when the potential of the video signal is higher than that of the conductive plate and the potential of the diode remains the same. Consequently, a leak current which flows from the pixel electrode of the pixel formation portion to the video signal line when the TFT is in the off state is suppressed.