In order to prevent a gradation shift due to variations in the thickness of a film used to form an auxiliary capacitor, a detection capacitor having a layer structure similar to that of the auxiliary capacitor placed for each pixel is provided on an array substrate. Furthermore, the capacitor value of the detection capacitor as a representative of the plurality of auxiliary capacitors is detected, and the potential amplitude ΔVcs of a power supply line connected to the auxiliary capacitor is adjusted based on this detected value.