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