A solid-state image pickup device includes a pixel unit configured to convert light into an electrical signal; a substrate having a first side on which the pixel unit is formed and a second side opposite the first side; an optical communication unit disposed on the first side of the substrate, and configured to convert a signal read out from the pixel unit into an optical signal and output the optical signal; and a cooling unit disposed on the second side of the substrate and below at least a forming area of the optical communication unit, the forming area being an area where the optical communication unit is formed, and configured to cool or dissipate heat generated in the optical communication unit and transferred through the substrate.