An image sensor may include a comparator including a first input terminal configured to receive a reset signal, a second input terminal configured to receive an image signal, a third input terminal configured to receive a ramp signal configured to ramp in one direction, and an output terminal. The comparator may further include a switch circuit including a plurality of switches. The comparator may be configured to compare the reset signal with the ramp signal and output a first comparison signal through the output terminal according to a first arrangement of the switches in a reset phase and the comparator may be configured to compare the image signal with the ramp signal and output a second comparison signal through the output terminal according to a second arrangement of the switches in an image phase.