The present disclosure relates to a solid-state image pickup device and an electronic apparatus by which a phase-difference detection pixel that avoids defects such as lowering of sensitivity to incident light and lowering of phase-difference detection accuracy can be realized. A solid-state image pickup device as a first aspect of the present disclosure is a solid-state image pickup device in which a normal pixel that generates a pixel signal of an image and a phase-difference detection pixel that generates a pixel signal used in calculation of a phase-difference signal for controlling an image-surface phase difference AF function are arranged in a mixed manner, in which, in the phase-difference detection pixel, a shared on-chip lens for condensing incident light to a photoelectric converter that generates a pixel signal used in calculation of the phase-difference signal is formed for every plurality of adjacent phase-difference detection pixels. The present disclosure is applicable to a backside illumination CMOS image sensor and an electronic apparatus equipped with the same.