In an image sensor having a plurality of pixels which photoelectrically convert a subject image, a plurality of pairs of focus detection pixels including first focus detection pixels (SHA) and second focus detection pixels (SHB) are arranged while being distributed. The layouts of the first focus detection pixel (SHA) and the second focus detection pixel (SHB) are switched in pairs of focus detection pixels adjacent in the focus detection direction. Focus detection is performed using image waveforms obtained from the first focus detection pixel (SHA) and the second focus detection pixel (SHB) whose layouts are switched. This reduces focus detection errors generated when the pixels included in the pairs of focus detection pixels receive light fluxes from different portions of the subject.