An image sensor includes a line sensor having sensor elements arranged in one line and configured to acquire, in each line cycle, R, G and B signals, when light sources, each corresponding to one of R, G and B colors, in the each line cycle, sequentially illuminate one after another in a predetermined order; a buffer having data saving units, each corresponding to one of the R, G and B colors; a controlling unit configured to generate, from the R, G and B signals, R, G and B data in each line cycle, and to add each of the R, G and B data in each cycle in a corresponding one of the data saving units; and an output unit configured to output to outside, as RGB line data, the R, G and B data in each line cycle that have been saved in the data saving units.