The invention provides a solid-state image pickup element including: a photodiode configured to convert incident light into a photocurrent; an amplification transistor configured to amplify a voltagebetween a gate having a potential depending on the photocurrent and a source having a predetermined reference potential and output the amplified voltage from a drain; and a potential supply section configured to supply an anode of the photodiode and a back-gate of the amplification transistor with a predetermined potential lower than the reference potential. The present invention also provides animage pickup apparatus including the solid-state image pickup element described above and a signal processing circuit configured to process a signal output from the amplification transistor.