An imaging element includes a first substrate provided with a photoelectric conversion unit configured to generate electric charges by photoelectric conversion and a signal line to which a signal based on the electric charges generated by the photoelectric conversion unit is output and a second substrate provided with a supply unit configured to supply a voltage to the signal line so that a voltage of the signal line does not fall below a predetermined voltage and a processing unit configured to process a signal output to the signal line, the second substrate being stacked on the first substrate.