The present invention provides a solid-state image sensor in which degradation in image quality can be reduced. The solid-state image sensor includes an optical isolation layer between a pupil dividing unit and a plurality of photoelectric conversion units. The optical isolation layer includes a plurality of high-refractive-index areas and a low-refractive-index area having a lower refractive index than that of the high-refractive-index areas. The high-refractive-index areas are disposed above the photoelectric conversion units, and the low-refractive-index area is disposed between the high-refractive-index areas. The refractive index changes stepwise at the boundaries between the high-refractive-index areas and the low-refractive-index area. The refractive index difference of the stepwise changing portion is 0.15 or more. A value obtained by multiplying the physical thickness of the optical isolation layer by the refractive index of the high-refractive-index areas is 2.0 or less times as large as the wavelength of incident light.