A signal for focus detection is generated by a first operation, in which a signal of at least one photoelectric conversion element included in a photoelectric conversion unit is read to an input node of an amplification unit and the signal is supplied to a common output line by the amplification unit and signals for forming an image are generated by a second operation, in which a signal of another photoelectric conversion element included in the same photoelectric conversion unit as that including the at least one photoelectric conversion element from which the signal has been read in the first operation is read to the input node of the amplification unit while holding the signal read in the first operation using the amplification unit and the signals are supplied to the common output line by the amplification unit.