To provide an image signal corrector which suitably corrects image signals outputted from imaging devices so as to effectively use an input range of an A/D converter circuit.

The corrector arithmetically computes a correction value VC according to an average VAV of image signals and a black level value VMB set by a user, and adds a pulse PC of a width corresponding to the correction value VC to the image signal. It clamps the signal with the added pulse PC and applies a knee process for compressing portions over a knee point. An A/D converter circuit 7 converts the processed signal to a digital signal. The corrector arithmetically computes difference between a corresponding value of the digital signal outputted from the converter circuit 7 to the top of the correction pulse PC and a specified value, and changes the clamp level so as to reduce the difference to '0'.