This invention improves charge transfer efficiency in a transfer gate having a vertical gate electrode. This solid-state imaging element comprises a photoelectric conversion unit, a charge accumulation unit, and the transfer gate. The photoelectric conversion unit is formed in the depth direction of a semiconductor substrate, and generates a charge in response to the amount of light received. The charge accumulation unit accumulates the charge generated by the photoelectric conversion unit. The transfer gate transfers the charges from the photoelectric conversion unit to the charge accumulation unit. The transfer gate comprises a plurality of vertical gate electrodes, each being embedded to a predetermined depth from the semiconductor substrate interface, and whereof at least a section in the semiconductor substrate depth direction has a different diameter.