This invention is to provide a solid-state image pickup apparatus including a photoelectric conversion unit (PD), transfer switch (MTX) for transferring signal charges from the photoelectric conversion unit, capacitance for holding the transferred signal charges, and amplification transistor (MSF) for outputting a signal corresponding to the signal charges held by the capacitance. The amplification transistor includes a capacitance unit (CFD) having the first capacitance value and an additive capacitance unit (Cox) for adding a capacitance to the capacitance unit to increase the first capacitance value and obtain the second capacitance value. A signal read-out from the amplification transistor has a first read-out mode in which a signal is read out while keeping the signal charges held by the capacitance unit and additive capacitance unit, and a second read-out mode in which a signal is read out while keeping the signal charges held by the capacitance unit.