An image sensor for high-speed data readout is provided. The image sensor includes a line memory block temporarily storing a digital signal in unit of lines which is generated based on an analog signal output from a pixel array. The line memory block includes a plurality of line memories, a plurality of data line pairs respectively connecting the line memories to a sense amplifying unit, and a plurality of data line prechargers each including at least two precharge units separately connected with a corresponding one of the data line pairs to precharge the corresponding data line pair with a predetermined precharge voltage. Accordingly, the image sensor performs high-speed digital signal readout based on precharge operation of the data line prechargers.