An image capturing apparatus is provided with a pixel array that has a plurality of image forming pixels and a plurality of focus detection pixels, a readout unit that reads out a pixel signal from the pixel array, an A/D conversion unit that has a first mode for A/D converting the pixel signal read out by the readout unit with a first resolution and a second mode for A/D converting the pixel signal read out by the readout unit with a second resolution that is higher than the first resolution, and a control unit that switches between the first mode and the second mode in accordance with the pixel signal read out from the pixel array.