An image sensor comprises: a pixel array having a plurality of photoelectric conversion portions provided for each of a plurality of microlenses arranged in matrix; a plurality of signal output lines provided for each column of the pixel array; signal readout circuits each provided for each column of the pixel array; and a control circuit that controls to output a signal of a selected row to one of the plurality of signal output lines and controls to process the signal by the corresponding signal readout circuit. The control circuit performs control such that while a signal of a first row output to one of the plurality of signal output lines is processed by the corresponding signal readout circuit, a signal from a second row is output to another of the plurality of signal output lines.