1. A lens shading correction device in an image sensor, the device comprising: a brightness weight storage unit configured to store a brightness weight for allowing one of representative brightness values of reference image blocks constituting a reference image to be a representative brightness value of a reference image block having a maximal representative brightness value among the reference image blocks; an input image divider configured to block and divide an input image into input image blocks, corresponding to the reference image blocks; and an input image brightness correction unit configured to correct a brightness of the input image by multiplying brightness of input pixels included in the input image blocks by brightness weights of the reference image blocks corresponding to the input image blocks.