1. An imaging sensor, comprising: a pixel array including: an active imaging portion configured to output a first signal corresponding to an amount of light incident on the pixel array, and a first shielded portion comprising a plurality of first shielded regions, the first shielded portion being shielded from light incident on the pixel array and configured to output a second signal; and a black-level adjustment circuit configured to adjust the first signal, comprising: an average value calculator configured to calculate an average signal value for each of the first shielded regions, a region selector configured to select average signal values that are within a predetermined range, and a black-level adjustment value calculator configured to calculate a black-level adjustment value by using average signal values selected by the region selector.