Image capturing apparatus

An image capturing apparatus comprising:

• a pixel array that has a plurality of unit pixels that each include a plurality of photoelectric conversion elements that receive light beams that have passed through different areas of an exit pupil of an imaging optical system;
• and
• one or more circuits configured to function as:
• 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 a magnitude relationship between a signal level of the pixel signal read out from the pixel array and a reference level,
• wherein the control unit changes the reference level between a case of combining signals of the plurality of photoelectric conversion elements in the unit pixel and reading out the combined signal and a case of independently reading out at least one signal of the plurality of photoelectrice conversion elements in the unit pixel.