Image capturing apparatus, driving method therefor, and image capturing system

An image capturing apparatus is provided. The apparatus comprises a pixel array, a signal generator that generates a comparison signal whose electric potential changes with time and a converter that converts a pixel signal into a digital signal. The comparison signal starts to change from a first electric potential in accordance with a start of the conversion of the pixel signal by the converter, and changes again, in accordance with inversion of a magnitude relationship between the pixel signal and the comparison signal, from a third electric potential between the first electric potential and a second electric potential at which the magnitude relationship is inverted. The converter includes a counter that holds, as a signal value, a count value obtained by counting from the start of the conversion of the pixel signal until the inversion of the magnitude relationship.