Disclosed is an image sensor. The image sensor includes an active pixel sensor array including first to fourth pixel units sequentially arranged in a column direction, and each of the first to fourth pixel units is composed of a plurality of pixels. A first pixel group including the first and second pixel units is connected to a first column line, and a second pixel group including the third pixel unit and the fourth pixel unit is connected to a second column line. The image sensor includes a correlated double sampling circuit including first and second correlated double samplers and configured to convert a first sense voltage sensed from a selected pixel of the first pixel group and a second sense voltage sensed from a selected pixel of the second pixel group into a first correlated double sampling signal and a second correlated double sampling signal, respectively.