The invention provides a comparator and a CMOS image sensor comprising the comparator. The comparator includes a comparison circuit including input ports to receive a pixel signal and a ramp signal, respectively, and structured to compare the pixel signal and the ramp signal to output a comparison signal; a sensing circuit coupled to the comparison circuit and structured to sense a common voltagevariation amount from the comparison circuit, wherein the common voltage variation amount depends on the pixel signal such that the common voltage variation amount increases as the pixel signal increases; and a tail current control circuit coupled to the sensing circuit and structured to control a tail current amount of the comparison circuit based on the common voltage variation amount.